1 /*
   2  * Copyright (c) 1998, 2024, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "classfile/vmSymbols.hpp"
  27 #include "gc/shared/oopStorage.hpp"
  28 #include "gc/shared/oopStorageSet.hpp"
  29 #include "jfr/jfrEvents.hpp"
  30 #include "jfr/support/jfrThreadId.hpp"
  31 #include "logging/log.hpp"
  32 #include "logging/logStream.hpp"
  33 #include "memory/allocation.inline.hpp"
  34 #include "memory/resourceArea.hpp"
  35 #include "oops/markWord.hpp"
  36 #include "oops/oop.inline.hpp"
  37 #include "oops/oopHandle.inline.hpp"
  38 #include "oops/weakHandle.inline.hpp"
  39 #include "prims/jvmtiDeferredUpdates.hpp"
  40 #include "prims/jvmtiExport.hpp"
  41 #include "runtime/atomic.hpp"
  42 #include "runtime/globals.hpp"
  43 #include "runtime/handles.inline.hpp"
  44 #include "runtime/interfaceSupport.inline.hpp"
  45 #include "runtime/javaThread.inline.hpp"
  46 #include "runtime/lightweightSynchronizer.hpp"
  47 #include "runtime/mutexLocker.hpp"
  48 #include "runtime/objectMonitor.hpp"
  49 #include "runtime/objectMonitor.inline.hpp"
  50 #include "runtime/orderAccess.hpp"
  51 #include "runtime/osThread.hpp"
  52 #include "runtime/perfData.hpp"
  53 #include "runtime/safefetch.hpp"
  54 #include "runtime/safepointMechanism.inline.hpp"
  55 #include "runtime/sharedRuntime.hpp"
  56 #include "runtime/synchronizer.hpp"
  57 #include "services/threadService.hpp"
  58 #include "utilities/debug.hpp"
  59 #include "utilities/dtrace.hpp"
  60 #include "utilities/globalDefinitions.hpp"
  61 #include "utilities/macros.hpp"
  62 #include "utilities/preserveException.hpp"
  63 #if INCLUDE_JFR
  64 #include "jfr/support/jfrFlush.hpp"
  65 #endif
  66 
  67 #ifdef DTRACE_ENABLED
  68 
  69 // Only bother with this argument setup if dtrace is available
  70 // TODO-FIXME: probes should not fire when caller is _blocked.  assert() accordingly.
  71 
  72 
  73 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread)                           \
  74   char* bytes = nullptr;                                                   \
  75   int len = 0;                                                             \
  76   jlong jtid = SharedRuntime::get_java_tid(thread);                        \
  77   Symbol* klassname = obj->klass()->name();                                \
  78   if (klassname != nullptr) {                                              \
  79     bytes = (char*)klassname->bytes();                                     \
  80     len = klassname->utf8_length();                                        \
  81   }
  82 
  83 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis)            \
  84   {                                                                        \
  85     if (DTraceMonitorProbes) {                                             \
  86       DTRACE_MONITOR_PROBE_COMMON(obj, thread);                            \
  87       HOTSPOT_MONITOR_WAIT(jtid,                                           \
  88                            (monitor), bytes, len, (millis));               \
  89     }                                                                      \
  90   }
  91 
  92 #define HOTSPOT_MONITOR_contended__enter HOTSPOT_MONITOR_CONTENDED_ENTER
  93 #define HOTSPOT_MONITOR_contended__entered HOTSPOT_MONITOR_CONTENDED_ENTERED
  94 #define HOTSPOT_MONITOR_contended__exit HOTSPOT_MONITOR_CONTENDED_EXIT
  95 #define HOTSPOT_MONITOR_notify HOTSPOT_MONITOR_NOTIFY
  96 #define HOTSPOT_MONITOR_notifyAll HOTSPOT_MONITOR_NOTIFYALL
  97 
  98 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread)                  \
  99   {                                                                        \
 100     if (DTraceMonitorProbes) {                                             \
 101       DTRACE_MONITOR_PROBE_COMMON(obj, thread);                            \
 102       HOTSPOT_MONITOR_##probe(jtid,                                        \
 103                               (uintptr_t)(monitor), bytes, len);           \
 104     }                                                                      \
 105   }
 106 
 107 #else //  ndef DTRACE_ENABLED
 108 
 109 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon)    {;}
 110 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon)          {;}
 111 
 112 #endif // ndef DTRACE_ENABLED
 113 
 114 DEBUG_ONLY(static volatile bool InitDone = false;)
 115 
 116 OopStorage* ObjectMonitor::_oop_storage = nullptr;
 117 
 118 // -----------------------------------------------------------------------------
 119 // Theory of operations -- Monitors lists, thread residency, etc:
 120 //
 121 // * A thread acquires ownership of a monitor by successfully
 122 //   CAS()ing the _owner field from null to non-null.
 123 //
 124 // * Invariant: A thread appears on at most one monitor list --
 125 //   cxq, EntryList or WaitSet -- at any one time.
 126 //
 127 // * Contending threads "push" themselves onto the cxq with CAS
 128 //   and then spin/park.
 129 //
 130 // * After a contending thread eventually acquires the lock it must
 131 //   dequeue itself from either the EntryList or the cxq.
 132 //
 133 // * The exiting thread identifies and unparks an "heir presumptive"
 134 //   tentative successor thread on the EntryList.  Critically, the
 135 //   exiting thread doesn't unlink the successor thread from the EntryList.
 136 //   After having been unparked, the wakee will recontend for ownership of
 137 //   the monitor.   The successor (wakee) will either acquire the lock or
 138 //   re-park itself.
 139 //
 140 //   Succession is provided for by a policy of competitive handoff.
 141 //   The exiting thread does _not_ grant or pass ownership to the
 142 //   successor thread.  (This is also referred to as "handoff" succession").
 143 //   Instead the exiting thread releases ownership and possibly wakes
 144 //   a successor, so the successor can (re)compete for ownership of the lock.
 145 //   If the EntryList is empty but the cxq is populated the exiting
 146 //   thread will drain the cxq into the EntryList.  It does so by
 147 //   by detaching the cxq (installing null with CAS) and folding
 148 //   the threads from the cxq into the EntryList.  The EntryList is
 149 //   doubly linked, while the cxq is singly linked because of the
 150 //   CAS-based "push" used to enqueue recently arrived threads (RATs).
 151 //
 152 // * Concurrency invariants:
 153 //
 154 //   -- only the monitor owner may access or mutate the EntryList.
 155 //      The mutex property of the monitor itself protects the EntryList
 156 //      from concurrent interference.
 157 //   -- Only the monitor owner may detach the cxq.
 158 //
 159 // * The monitor entry list operations avoid locks, but strictly speaking
 160 //   they're not lock-free.  Enter is lock-free, exit is not.
 161 //   For a description of 'Methods and apparatus providing non-blocking access
 162 //   to a resource,' see U.S. Pat. No. 7844973.
 163 //
 164 // * The cxq can have multiple concurrent "pushers" but only one concurrent
 165 //   detaching thread.  This mechanism is immune from the ABA corruption.
 166 //   More precisely, the CAS-based "push" onto cxq is ABA-oblivious.
 167 //
 168 // * Taken together, the cxq and the EntryList constitute or form a
 169 //   single logical queue of threads stalled trying to acquire the lock.
 170 //   We use two distinct lists to improve the odds of a constant-time
 171 //   dequeue operation after acquisition (in the ::enter() epilogue) and
 172 //   to reduce heat on the list ends.  (c.f. Michael Scott's "2Q" algorithm).
 173 //   A key desideratum is to minimize queue & monitor metadata manipulation
 174 //   that occurs while holding the monitor lock -- that is, we want to
 175 //   minimize monitor lock holds times.  Note that even a small amount of
 176 //   fixed spinning will greatly reduce the # of enqueue-dequeue operations
 177 //   on EntryList|cxq.  That is, spinning relieves contention on the "inner"
 178 //   locks and monitor metadata.
 179 //
 180 //   Cxq points to the set of Recently Arrived Threads attempting entry.
 181 //   Because we push threads onto _cxq with CAS, the RATs must take the form of
 182 //   a singly-linked LIFO.  We drain _cxq into EntryList  at unlock-time when
 183 //   the unlocking thread notices that EntryList is null but _cxq is != null.
 184 //
 185 //   The EntryList is ordered by the prevailing queue discipline and
 186 //   can be organized in any convenient fashion, such as a doubly-linked list or
 187 //   a circular doubly-linked list.  Critically, we want insert and delete operations
 188 //   to operate in constant-time.  If we need a priority queue then something akin
 189 //   to Solaris' sleepq would work nicely.  Viz.,
 190 //   http://agg.eng/ws/on10_nightly/source/usr/src/uts/common/os/sleepq.c.
 191 //   Queue discipline is enforced at ::exit() time, when the unlocking thread
 192 //   drains the cxq into the EntryList, and orders or reorders the threads on the
 193 //   EntryList accordingly.
 194 //
 195 //   Barring "lock barging", this mechanism provides fair cyclic ordering,
 196 //   somewhat similar to an elevator-scan.
 197 //
 198 // * The monitor synchronization subsystem avoids the use of native
 199 //   synchronization primitives except for the narrow platform-specific
 200 //   park-unpark abstraction.  See the comments in os_solaris.cpp regarding
 201 //   the semantics of park-unpark.  Put another way, this monitor implementation
 202 //   depends only on atomic operations and park-unpark.  The monitor subsystem
 203 //   manages all RUNNING->BLOCKED and BLOCKED->READY transitions while the
 204 //   underlying OS manages the READY<->RUN transitions.
 205 //
 206 // * Waiting threads reside on the WaitSet list -- wait() puts
 207 //   the caller onto the WaitSet.
 208 //
 209 // * notify() or notifyAll() simply transfers threads from the WaitSet to
 210 //   either the EntryList or cxq.  Subsequent exit() operations will
 211 //   unpark the notifyee.  Unparking a notifee in notify() is inefficient -
 212 //   it's likely the notifyee would simply impale itself on the lock held
 213 //   by the notifier.
 214 //
 215 // * An interesting alternative is to encode cxq as (List,LockByte) where
 216 //   the LockByte is 0 iff the monitor is owned.  _owner is simply an auxiliary
 217 //   variable, like _recursions, in the scheme.  The threads or Events that form
 218 //   the list would have to be aligned in 256-byte addresses.  A thread would
 219 //   try to acquire the lock or enqueue itself with CAS, but exiting threads
 220 //   could use a 1-0 protocol and simply STB to set the LockByte to 0.
 221 //   Note that is is *not* word-tearing, but it does presume that full-word
 222 //   CAS operations are coherent with intermix with STB operations.  That's true
 223 //   on most common processors.
 224 //
 225 // * See also http://blogs.sun.com/dave
 226 
 227 
 228 // Check that object() and set_object() are called from the right context:
 229 static void check_object_context() {
 230 #ifdef ASSERT
 231   Thread* self = Thread::current();
 232   if (self->is_Java_thread()) {
 233     // Mostly called from JavaThreads so sanity check the thread state.
 234     JavaThread* jt = JavaThread::cast(self);
 235     switch (jt->thread_state()) {
 236     case _thread_in_vm:    // the usual case
 237     case _thread_in_Java:  // during deopt
 238       break;
 239     default:
 240       fatal("called from an unsafe thread state");
 241     }
 242     assert(jt->is_active_Java_thread(), "must be active JavaThread");
 243   } else {
 244     // However, ThreadService::get_current_contended_monitor()
 245     // can call here via the VMThread so sanity check it.
 246     assert(self->is_VM_thread(), "must be");
 247   }
 248 #endif // ASSERT
 249 }
 250 
 251 ObjectMonitor::ObjectMonitor(oop object) :
 252   _metadata(0),
 253   _object(_oop_storage, object),
 254   _owner(nullptr),
 255   _previous_owner_tid(0),
 256   _next_om(nullptr),
 257   _recursions(0),
 258   _EntryList(nullptr),
 259   _cxq(nullptr),
 260   _succ(nullptr),
 261   _Responsible(nullptr),
 262   _SpinDuration(ObjectMonitor::Knob_SpinLimit),
 263   _contentions(0),
 264   _WaitSet(nullptr),
 265   _waiters(0),
 266   _WaitSetLock(0)
 267 { }
 268 
 269 ObjectMonitor::~ObjectMonitor() {
 270   _object.release(_oop_storage);
 271 }
 272 
 273 oop ObjectMonitor::object() const {
 274   check_object_context();
 275   return _object.resolve();
 276 }
 277 




 278 void ObjectMonitor::ExitOnSuspend::operator()(JavaThread* current) {
 279   if (current->is_suspended()) {
 280     _om->_recursions = 0;
 281     _om->_succ = nullptr;
 282     // Don't need a full fence after clearing successor here because of the call to exit().
 283     _om->exit(current, false /* not_suspended */);
 284     _om_exited = true;
 285 
 286     current->set_current_pending_monitor(_om);
 287   }
 288 }
 289 
 290 void ObjectMonitor::ClearSuccOnSuspend::operator()(JavaThread* current) {
 291   if (current->is_suspended()) {
 292     if (_om->_succ == current) {
 293       _om->_succ = nullptr;
 294       OrderAccess::fence(); // always do a full fence when successor is cleared
 295     }
 296   }
 297 }
 298 
 299 #define assert_mark_word_consistency()                                         \
 300   assert(UseObjectMonitorTable || object()->mark() == markWord::encode(this),  \
 301          "object mark must match encoded this: mark=" INTPTR_FORMAT            \
 302          ", encoded this=" INTPTR_FORMAT, object()->mark().value(),            \
 303          markWord::encode(this).value());
 304 
 305 // -----------------------------------------------------------------------------
 306 // Enter support
 307 
 308 bool ObjectMonitor::enter_is_async_deflating() {
 309   if (is_being_async_deflated()) {
 310     if (!UseObjectMonitorTable) {
 311       const oop l_object = object();
 312       if (l_object != nullptr) {
 313         // Attempt to restore the header/dmw to the object's header so that
 314         // we only retry once if the deflater thread happens to be slow.
 315         install_displaced_markword_in_object(l_object);
 316       }
 317     }
 318     return true;
 319   }
 320 
 321   return false;
 322 }
 323 
 324 void ObjectMonitor::enter_for_with_contention_mark(JavaThread* locking_thread, ObjectMonitorContentionMark& contention_mark) {
 325   // Used by ObjectSynchronizer::enter_for to enter for another thread.
 326   // The monitor is private to or already owned by locking_thread which must be suspended.
 327   // So this code may only contend with deflation.
 328   assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
 329   assert(contention_mark._monitor == this, "must be");
 330   assert(!is_being_async_deflated(), "must be");
 331 
 332 
 333   void* prev_owner = try_set_owner_from(nullptr, locking_thread);
 334 
 335   bool success = false;


 336 
 337   if (prev_owner == nullptr) {
 338     assert(_recursions == 0, "invariant");
 339     success = true;
 340   } else if (prev_owner == locking_thread) {
 341     _recursions++;
 342     success = true;
 343   } else if (prev_owner == DEFLATER_MARKER) {
 344     // Racing with deflation.
 345     prev_owner = try_set_owner_from(DEFLATER_MARKER, locking_thread);
 346     if (prev_owner == DEFLATER_MARKER) {
 347       // Cancelled deflation. Increment contentions as part of the deflation protocol.
 348       add_to_contentions(1);













 349       success = true;
 350     } else if (prev_owner == nullptr) {
 351       // At this point we cannot race with deflation as we have both incremented
 352       // contentions, seen contention > 0 and seen a DEFLATER_MARKER.
 353       // success will only be false if this races with something other than
 354       // deflation.
 355       prev_owner = try_set_owner_from(nullptr, locking_thread);
 356       success = prev_owner == nullptr;
 357     }
 358   } else if (LockingMode == LM_LEGACY && locking_thread->is_lock_owned((address)prev_owner)) {
 359     assert(_recursions == 0, "must be");
 360     _recursions = 1;
 361     set_owner_from_BasicLock(prev_owner, locking_thread);
 362     success = true;








 363   }
 364   assert(success, "Failed to enter_for: locking_thread=" INTPTR_FORMAT
 365           ", this=" INTPTR_FORMAT "{owner=" INTPTR_FORMAT "}, observed owner: " INTPTR_FORMAT,
 366           p2i(locking_thread), p2i(this), p2i(owner_raw()), p2i(prev_owner));
 367 }
 368 
 369 bool ObjectMonitor::enter_for(JavaThread* locking_thread) {
 370 
 371   // Block out deflation as soon as possible.
 372   ObjectMonitorContentionMark contention_mark(this);
 373 
 374   // Check for deflation.
 375   if (enter_is_async_deflating()) {
 376     return false;
 377   }
 378 
 379   enter_for_with_contention_mark(locking_thread, contention_mark);
 380   assert(owner_raw() == locking_thread, "must be");
 381   return true;
 382 }
 383 
 384 bool ObjectMonitor::try_enter(JavaThread* current) {
 385   // TryLock avoids the CAS
 386   TryLockResult r = TryLock(current);
 387   if (r == TryLockResult::Success) {



 388     assert(_recursions == 0, "invariant");
 389     return true;
 390   }
 391 
 392   if (r == TryLockResult::HasOwner && owner() == current) {

 393     _recursions++;
 394     return true;
 395   }
 396 
 397   void* cur = owner_raw();
 398   if (LockingMode == LM_LEGACY && current->is_lock_owned((address)cur)) {
 399     assert(_recursions == 0, "internal state error");
 400     _recursions = 1;
 401     set_owner_from_BasicLock(cur, current);  // Convert from BasicLock* to Thread*.
 402     return true;
 403   }
 404 
 405   return false;
 406 }
 407 
 408 bool ObjectMonitor::spin_enter(JavaThread* current) {
 409   assert(current == JavaThread::current(), "must be");
 410 
 411   // Check for recursion.
 412   if (try_enter(current)) {
 413     return true;
 414   }
 415 
 416   // Check for deflation.
 417   if (enter_is_async_deflating()) {
 418     return false;
 419   }
 420 
 421   // We've encountered genuine contention.
 422 
 423   // Do one round of spinning.


 424   // Note that if we acquire the monitor from an initial spin
 425   // we forgo posting JVMTI events and firing DTRACE probes.
 426   if (TrySpin(current)) {
 427     assert(owner_raw() == current, "must be current: owner=" INTPTR_FORMAT, p2i(owner_raw()));
 428     assert(_recursions == 0, "must be 0: recursions=" INTX_FORMAT, _recursions);
 429     assert_mark_word_consistency();
 430     return true;
 431   }
 432 
 433   return false;
 434 }
 435 
 436 bool ObjectMonitor::enter(JavaThread* current) {
 437   assert(current == JavaThread::current(), "must be");
 438 
 439   if (spin_enter(current)) {
 440     return true;
 441   }
 442 
 443   assert(owner_raw() != current, "invariant");
 444   assert(_succ != current, "invariant");
 445   assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
 446   assert(current->thread_state() != _thread_blocked, "invariant");
 447 
 448   // Keep is_being_async_deflated stable across the rest of enter
 449   ObjectMonitorContentionMark contention_mark(this);
 450 
 451   // Check for deflation.
 452   if (enter_is_async_deflating()) {








 453     return false;
 454   }
 455 
 456   // At this point this ObjectMonitor cannot be deflated, finish contended enter
 457   enter_with_contention_mark(current, contention_mark);
 458   return true;
 459 }
 460 
 461 void ObjectMonitor::enter_with_contention_mark(JavaThread *current, ObjectMonitorContentionMark &cm) {
 462   assert(current == JavaThread::current(), "must be");
 463   assert(owner_raw() != current, "must be");
 464   assert(cm._monitor == this, "must be");
 465   assert(!is_being_async_deflated(), "must be");
 466 
 467   JFR_ONLY(JfrConditionalFlush<EventJavaMonitorEnter> flush(current);)
 468   EventJavaMonitorEnter event;
 469   if (event.is_started()) {
 470     event.set_monitorClass(object()->klass());
 471     // Set an address that is 'unique enough', such that events close in
 472     // time and with the same address are likely (but not guaranteed) to
 473     // belong to the same object.
 474     event.set_address((uintptr_t)this);
 475   }
 476 
 477   { // Change java thread status to indicate blocked on monitor enter.
 478     JavaThreadBlockedOnMonitorEnterState jtbmes(current, this);
 479 
 480     assert(current->current_pending_monitor() == nullptr, "invariant");
 481     current->set_current_pending_monitor(this);
 482 
 483     DTRACE_MONITOR_PROBE(contended__enter, this, object(), current);
 484     if (JvmtiExport::should_post_monitor_contended_enter()) {
 485       JvmtiExport::post_monitor_contended_enter(current, this);
 486 
 487       // The current thread does not yet own the monitor and does not
 488       // yet appear on any queues that would get it made the successor.
 489       // This means that the JVMTI_EVENT_MONITOR_CONTENDED_ENTER event
 490       // handler cannot accidentally consume an unpark() meant for the
 491       // ParkEvent associated with this ObjectMonitor.
 492     }
 493 
 494     OSThreadContendState osts(current->osthread());
 495 
 496     assert(current->thread_state() == _thread_in_vm, "invariant");
 497 
 498     for (;;) {
 499       ExitOnSuspend eos(this);
 500       {
 501         ThreadBlockInVMPreprocess<ExitOnSuspend> tbivs(current, eos, true /* allow_suspend */);
 502         EnterI(current);
 503         current->set_current_pending_monitor(nullptr);
 504         // We can go to a safepoint at the end of this block. If we
 505         // do a thread dump during that safepoint, then this thread will show
 506         // as having "-locked" the monitor, but the OS and java.lang.Thread
 507         // states will still report that the thread is blocked trying to
 508         // acquire it.
 509         // If there is a suspend request, ExitOnSuspend will exit the OM
 510         // and set the OM as pending.
 511       }
 512       if (!eos.exited()) {
 513         // ExitOnSuspend did not exit the OM
 514         assert(owner_raw() == current, "invariant");
 515         break;
 516       }
 517     }
 518 
 519     // We've just gotten past the enter-check-for-suspend dance and we now own
 520     // the monitor free and clear.
 521   }
 522 

 523   assert(contentions() >= 0, "must not be negative: contentions=%d", contentions());
 524 
 525   // Must either set _recursions = 0 or ASSERT _recursions == 0.
 526   assert(_recursions == 0, "invariant");
 527   assert(owner_raw() == current, "invariant");
 528   assert(_succ != current, "invariant");
 529   assert_mark_word_consistency();
 530 
 531   // The thread -- now the owner -- is back in vm mode.
 532   // Report the glorious news via TI,DTrace and jvmstat.
 533   // The probe effect is non-trivial.  All the reportage occurs
 534   // while we hold the monitor, increasing the length of the critical
 535   // section.  Amdahl's parallel speedup law comes vividly into play.
 536   //
 537   // Another option might be to aggregate the events (thread local or
 538   // per-monitor aggregation) and defer reporting until a more opportune
 539   // time -- such as next time some thread encounters contention but has
 540   // yet to acquire the lock.  While spinning that thread could
 541   // spinning we could increment JVMStat counters, etc.
 542 
 543   DTRACE_MONITOR_PROBE(contended__entered, this, object(), current);
 544   if (JvmtiExport::should_post_monitor_contended_entered()) {
 545     JvmtiExport::post_monitor_contended_entered(current, this);
 546 
 547     // The current thread already owns the monitor and is not going to
 548     // call park() for the remainder of the monitor enter protocol. So
 549     // it doesn't matter if the JVMTI_EVENT_MONITOR_CONTENDED_ENTERED
 550     // event handler consumed an unpark() issued by the thread that
 551     // just exited the monitor.
 552   }
 553   if (event.should_commit()) {
 554     event.set_previousOwner(_previous_owner_tid);
 555     event.commit();
 556   }
 557   OM_PERFDATA_OP(ContendedLockAttempts, inc());

 558 }
 559 
 560 // Caveat: TryLock() is not necessarily serializing if it returns failure.
 561 // Callers must compensate as needed.
 562 
 563 ObjectMonitor::TryLockResult ObjectMonitor::TryLock(JavaThread* current) {
 564   void* own = owner_raw();
 565   if (own != nullptr) return TryLockResult::HasOwner;
 566   if (try_set_owner_from(nullptr, current) == nullptr) {
 567     assert(_recursions == 0, "invariant");
 568     return TryLockResult::Success;
 569   }
 570   // The lock had been free momentarily, but we lost the race to the lock.
 571   // Interference -- the CAS failed.
 572   // We can either return -1 or retry.
 573   // Retry doesn't make as much sense because the lock was just acquired.
 574   return TryLockResult::Interference;
 575 }
 576 
 577 // Deflate the specified ObjectMonitor if not in-use. Returns true if it
 578 // was deflated and false otherwise.
 579 //
 580 // The async deflation protocol sets owner to DEFLATER_MARKER and
 581 // makes contentions negative as signals to contending threads that
 582 // an async deflation is in progress. There are a number of checks
 583 // as part of the protocol to make sure that the calling thread has
 584 // not lost the race to a contending thread.
 585 //
 586 // The ObjectMonitor has been successfully async deflated when:
 587 //   (contentions < 0)
 588 // Contending threads that see that condition know to retry their operation.
 589 //
 590 bool ObjectMonitor::deflate_monitor(Thread* current) {
 591   if (is_busy()) {
 592     // Easy checks are first - the ObjectMonitor is busy so no deflation.
 593     return false;
 594   }
 595 
 596   const oop obj = object_peek();
 597 
 598   if (obj == nullptr) {
 599     // If the object died, we can recycle the monitor without racing with
 600     // Java threads. The GC already broke the association with the object.
 601     set_owner_from(nullptr, DEFLATER_MARKER);
 602     assert(contentions() >= 0, "must be non-negative: contentions=%d", contentions());
 603     _contentions = INT_MIN; // minimum negative int
 604   } else {
 605     // Attempt async deflation protocol.
 606 
 607     // Set a null owner to DEFLATER_MARKER to force any contending thread
 608     // through the slow path. This is just the first part of the async
 609     // deflation dance.
 610     if (try_set_owner_from(nullptr, DEFLATER_MARKER) != nullptr) {
 611       // The owner field is no longer null so we lost the race since the
 612       // ObjectMonitor is now busy.
 613       return false;
 614     }
 615 
 616     if (contentions() > 0 || _waiters != 0) {
 617       // Another thread has raced to enter the ObjectMonitor after
 618       // is_busy() above or has already entered and waited on
 619       // it which makes it busy so no deflation. Restore owner to
 620       // null if it is still DEFLATER_MARKER.
 621       if (try_set_owner_from(DEFLATER_MARKER, nullptr) != DEFLATER_MARKER) {
 622         // Deferred decrement for the JT EnterI() that cancelled the async deflation.
 623         add_to_contentions(-1);
 624       }
 625       return false;
 626     }
 627 
 628     // Make a zero contentions field negative to force any contending threads
 629     // to retry. This is the second part of the async deflation dance.
 630     if (Atomic::cmpxchg(&_contentions, 0, INT_MIN) != 0) {
 631       // Contentions was no longer 0 so we lost the race since the
 632       // ObjectMonitor is now busy. Restore owner to null if it is
 633       // still DEFLATER_MARKER:
 634       if (try_set_owner_from(DEFLATER_MARKER, nullptr) != DEFLATER_MARKER) {
 635         // Deferred decrement for the JT EnterI() that cancelled the async deflation.
 636         add_to_contentions(-1);
 637       }
 638       return false;
 639     }
 640   }
 641 
 642   // Sanity checks for the races:
 643   guarantee(owner_is_DEFLATER_MARKER(), "must be deflater marker");
 644   guarantee(contentions() < 0, "must be negative: contentions=%d",
 645             contentions());
 646   guarantee(_waiters == 0, "must be 0: waiters=%d", _waiters);
 647   guarantee(_cxq == nullptr, "must be no contending threads: cxq="
 648             INTPTR_FORMAT, p2i(_cxq));
 649   guarantee(_EntryList == nullptr,
 650             "must be no entering threads: EntryList=" INTPTR_FORMAT,
 651             p2i(_EntryList));
 652 
 653   if (obj != nullptr) {
 654     if (log_is_enabled(Trace, monitorinflation)) {
 655       ResourceMark rm;
 656       log_trace(monitorinflation)("deflate_monitor: object=" INTPTR_FORMAT
 657                                   ", mark=" INTPTR_FORMAT ", type='%s'",
 658                                   p2i(obj), obj->mark().value(),
 659                                   obj->klass()->external_name());
 660     }
 661   }
 662 
 663   if (UseObjectMonitorTable) {
 664     LightweightSynchronizer::deflate_monitor(current, obj, this);
 665   } else {
 666     if (obj != nullptr) {
 667       // Install the old mark word if nobody else has already done it.
 668       install_displaced_markword_in_object(obj);
 669     }
 670   }
 671 
 672   // We leave owner == DEFLATER_MARKER and contentions < 0
 673   // to force any racing threads to retry.
 674   return true;  // Success, ObjectMonitor has been deflated.
 675 }
 676 
 677 // Install the displaced mark word (dmw) of a deflating ObjectMonitor
 678 // into the header of the object associated with the monitor. This
 679 // idempotent method is called by a thread that is deflating a
 680 // monitor and by other threads that have detected a race with the
 681 // deflation process.
 682 void ObjectMonitor::install_displaced_markword_in_object(const oop obj) {
 683   assert(!UseObjectMonitorTable, "Lightweight has no dmw");
 684   // This function must only be called when (owner == DEFLATER_MARKER
 685   // && contentions <= 0), but we can't guarantee that here because
 686   // those values could change when the ObjectMonitor gets moved from
 687   // the global free list to a per-thread free list.
 688 
 689   guarantee(obj != nullptr, "must be non-null");
 690 
 691   // Separate loads in is_being_async_deflated(), which is almost always
 692   // called before this function, from the load of dmw/header below.
 693 
 694   // _contentions and dmw/header may get written by different threads.
 695   // Make sure to observe them in the same order when having several observers.
 696   OrderAccess::loadload_for_IRIW();
 697 
 698   const oop l_object = object_peek();
 699   if (l_object == nullptr) {
 700     // ObjectMonitor's object ref has already been cleared by async
 701     // deflation or GC so we're done here.
 702     return;
 703   }
 704   assert(l_object == obj, "object=" INTPTR_FORMAT " must equal obj="
 705          INTPTR_FORMAT, p2i(l_object), p2i(obj));
 706 
 707   markWord dmw = header();
 708   // The dmw has to be neutral (not null, not locked and not marked).
 709   assert(dmw.is_neutral(), "must be neutral: dmw=" INTPTR_FORMAT, dmw.value());
 710 
 711   // Install displaced mark word if the object's header still points
 712   // to this ObjectMonitor. More than one racing caller to this function
 713   // can rarely reach this point, but only one can win.
 714   markWord res = obj->cas_set_mark(dmw, markWord::encode(this));
 715   if (res != markWord::encode(this)) {
 716     // This should be rare so log at the Info level when it happens.
 717     log_info(monitorinflation)("install_displaced_markword_in_object: "
 718                                "failed cas_set_mark: new_mark=" INTPTR_FORMAT
 719                                ", old_mark=" INTPTR_FORMAT ", res=" INTPTR_FORMAT,
 720                                dmw.value(), markWord::encode(this).value(),
 721                                res.value());
 722   }
 723 
 724   // Note: It does not matter which thread restored the header/dmw
 725   // into the object's header. The thread deflating the monitor just
 726   // wanted the object's header restored and it is. The threads that
 727   // detected a race with the deflation process also wanted the
 728   // object's header restored before they retry their operation and
 729   // because it is restored they will only retry once.
 730 }
 731 
 732 // Convert the fields used by is_busy() to a string that can be
 733 // used for diagnostic output.
 734 const char* ObjectMonitor::is_busy_to_string(stringStream* ss) {
 735   ss->print("is_busy: waiters=%d"
 736             ", contentions=%d"
 737             ", owner=" PTR_FORMAT
 738             ", cxq=" PTR_FORMAT
 739             ", EntryList=" PTR_FORMAT,
 740             _waiters,
 741             (contentions() > 0 ? contentions() : 0),
 742             owner_is_DEFLATER_MARKER()
 743                 // We report null instead of DEFLATER_MARKER here because is_busy()
 744                 // ignores DEFLATER_MARKER values.
 745                 ? p2i(nullptr)
 746                 : p2i(owner_raw()),
 747             p2i(_cxq),
 748             p2i(_EntryList));
 749   return ss->base();
 750 }
 751 
 752 #define MAX_RECHECK_INTERVAL 1000
 753 
 754 void ObjectMonitor::EnterI(JavaThread* current) {
 755   assert(current->thread_state() == _thread_blocked, "invariant");
 756 
 757   // Try the lock - TATAS
 758   if (TryLock(current) == TryLockResult::Success) {
 759     assert(_succ != current, "invariant");
 760     assert(owner_raw() == current, "invariant");
 761     assert(_Responsible != current, "invariant");
 762     return;
 763   }
 764 
 765   if (try_set_owner_from(DEFLATER_MARKER, current) == DEFLATER_MARKER) {
 766     // Cancelled the in-progress async deflation by changing owner from
 767     // DEFLATER_MARKER to current. As part of the contended enter protocol,
 768     // contentions was incremented to a positive value before EnterI()
 769     // was called and that prevents the deflater thread from winning the
 770     // last part of the 2-part async deflation protocol. After EnterI()
 771     // returns to enter(), contentions is decremented because the caller
 772     // now owns the monitor. We bump contentions an extra time here to
 773     // prevent the deflater thread from winning the last part of the
 774     // 2-part async deflation protocol after the regular decrement
 775     // occurs in enter(). The deflater thread will decrement contentions
 776     // after it recognizes that the async deflation was cancelled.
 777     add_to_contentions(1);
 778     assert(_succ != current, "invariant");
 779     assert(_Responsible != current, "invariant");
 780     return;
 781   }
 782 
 783   assert(InitDone, "Unexpectedly not initialized");
 784 
 785   // We try one round of spinning *before* enqueueing current.
 786   //
 787   // If the _owner is ready but OFFPROC we could use a YieldTo()
 788   // operation to donate the remainder of this thread's quantum
 789   // to the owner.  This has subtle but beneficial affinity
 790   // effects.
 791 
 792   if (TrySpin(current)) {
 793     assert(owner_raw() == current, "invariant");
 794     assert(_succ != current, "invariant");
 795     assert(_Responsible != current, "invariant");
 796     return;
 797   }
 798 
 799   // The Spin failed -- Enqueue and park the thread ...
 800   assert(_succ != current, "invariant");
 801   assert(owner_raw() != current, "invariant");
 802   assert(_Responsible != current, "invariant");
 803 
 804   // Enqueue "current" on ObjectMonitor's _cxq.
 805   //
 806   // Node acts as a proxy for current.
 807   // As an aside, if were to ever rewrite the synchronization code mostly
 808   // in Java, WaitNodes, ObjectMonitors, and Events would become 1st-class
 809   // Java objects.  This would avoid awkward lifecycle and liveness issues,
 810   // as well as eliminate a subset of ABA issues.
 811   // TODO: eliminate ObjectWaiter and enqueue either Threads or Events.
 812 
 813   ObjectWaiter node(current);
 814   current->_ParkEvent->reset();
 815   node._prev   = (ObjectWaiter*) 0xBAD;
 816   node.TState  = ObjectWaiter::TS_CXQ;
 817 
 818   // Push "current" onto the front of the _cxq.
 819   // Once on cxq/EntryList, current stays on-queue until it acquires the lock.
 820   // Note that spinning tends to reduce the rate at which threads
 821   // enqueue and dequeue on EntryList|cxq.
 822   ObjectWaiter* nxt;
 823   for (;;) {
 824     node._next = nxt = _cxq;
 825     if (Atomic::cmpxchg(&_cxq, nxt, &node) == nxt) break;
 826 
 827     // Interference - the CAS failed because _cxq changed.  Just retry.
 828     // As an optional optimization we retry the lock.
 829     if (TryLock(current) == TryLockResult::Success) {
 830       assert(_succ != current, "invariant");
 831       assert(owner_raw() == current, "invariant");
 832       assert(_Responsible != current, "invariant");
 833       return;
 834     }
 835   }
 836 
 837   // Check for cxq|EntryList edge transition to non-null.  This indicates
 838   // the onset of contention.  While contention persists exiting threads
 839   // will use a ST:MEMBAR:LD 1-1 exit protocol.  When contention abates exit
 840   // operations revert to the faster 1-0 mode.  This enter operation may interleave
 841   // (race) a concurrent 1-0 exit operation, resulting in stranding, so we
 842   // arrange for one of the contending thread to use a timed park() operations
 843   // to detect and recover from the race.  (Stranding is form of progress failure
 844   // where the monitor is unlocked but all the contending threads remain parked).
 845   // That is, at least one of the contended threads will periodically poll _owner.
 846   // One of the contending threads will become the designated "Responsible" thread.
 847   // The Responsible thread uses a timed park instead of a normal indefinite park
 848   // operation -- it periodically wakes and checks for and recovers from potential
 849   // strandings admitted by 1-0 exit operations.   We need at most one Responsible
 850   // thread per-monitor at any given moment.  Only threads on cxq|EntryList may
 851   // be responsible for a monitor.
 852   //
 853   // Currently, one of the contended threads takes on the added role of "Responsible".
 854   // A viable alternative would be to use a dedicated "stranding checker" thread
 855   // that periodically iterated over all the threads (or active monitors) and unparked
 856   // successors where there was risk of stranding.  This would help eliminate the
 857   // timer scalability issues we see on some platforms as we'd only have one thread
 858   // -- the checker -- parked on a timer.
 859 
 860   if (nxt == nullptr && _EntryList == nullptr) {
 861     // Try to assume the role of responsible thread for the monitor.
 862     // CONSIDER:  ST vs CAS vs { if (Responsible==null) Responsible=current }
 863     Atomic::replace_if_null(&_Responsible, current);
 864   }
 865 
 866   // The lock might have been released while this thread was occupied queueing
 867   // itself onto _cxq.  To close the race and avoid "stranding" and
 868   // progress-liveness failure we must resample-retry _owner before parking.
 869   // Note the Dekker/Lamport duality: ST cxq; MEMBAR; LD Owner.
 870   // In this case the ST-MEMBAR is accomplished with CAS().
 871   //
 872   // TODO: Defer all thread state transitions until park-time.
 873   // Since state transitions are heavy and inefficient we'd like
 874   // to defer the state transitions until absolutely necessary,
 875   // and in doing so avoid some transitions ...
 876 
 877   int recheckInterval = 1;
 878 
 879   for (;;) {
 880 
 881     if (TryLock(current) == TryLockResult::Success) {
 882       break;
 883     }
 884     assert(owner_raw() != current, "invariant");
 885 
 886     // park self
 887     if (_Responsible == current) {
 888       current->_ParkEvent->park((jlong) recheckInterval);
 889       // Increase the recheckInterval, but clamp the value.
 890       recheckInterval *= 8;
 891       if (recheckInterval > MAX_RECHECK_INTERVAL) {
 892         recheckInterval = MAX_RECHECK_INTERVAL;
 893       }
 894     } else {
 895       current->_ParkEvent->park();
 896     }
 897 
 898     if (TryLock(current) == TryLockResult::Success) {
 899       break;
 900     }
 901 
 902     if (try_set_owner_from(DEFLATER_MARKER, current) == DEFLATER_MARKER) {
 903       // Cancelled the in-progress async deflation by changing owner from
 904       // DEFLATER_MARKER to current. As part of the contended enter protocol,
 905       // contentions was incremented to a positive value before EnterI()
 906       // was called and that prevents the deflater thread from winning the
 907       // last part of the 2-part async deflation protocol. After EnterI()
 908       // returns to enter(), contentions is decremented because the caller
 909       // now owns the monitor. We bump contentions an extra time here to
 910       // prevent the deflater thread from winning the last part of the
 911       // 2-part async deflation protocol after the regular decrement
 912       // occurs in enter(). The deflater thread will decrement contentions
 913       // after it recognizes that the async deflation was cancelled.
 914       add_to_contentions(1);
 915       break;
 916     }
 917 
 918     // The lock is still contested.
 919 
 920     // Keep a tally of the # of futile wakeups.
 921     // Note that the counter is not protected by a lock or updated by atomics.
 922     // That is by design - we trade "lossy" counters which are exposed to
 923     // races during updates for a lower probe effect.
 924     // This PerfData object can be used in parallel with a safepoint.
 925     // See the work around in PerfDataManager::destroy().
 926     OM_PERFDATA_OP(FutileWakeups, inc());
 927 
 928     // Assuming this is not a spurious wakeup we'll normally find _succ == current.
 929     // We can defer clearing _succ until after the spin completes
 930     // TrySpin() must tolerate being called with _succ == current.
 931     // Try yet another round of adaptive spinning.
 932     if (TrySpin(current)) {
 933       break;
 934     }
 935 
 936     // We can find that we were unpark()ed and redesignated _succ while
 937     // we were spinning.  That's harmless.  If we iterate and call park(),
 938     // park() will consume the event and return immediately and we'll
 939     // just spin again.  This pattern can repeat, leaving _succ to simply
 940     // spin on a CPU.
 941 
 942     if (_succ == current) _succ = nullptr;
 943 
 944     // Invariant: after clearing _succ a thread *must* retry _owner before parking.
 945     OrderAccess::fence();
 946   }
 947 
 948   // Egress :
 949   // current has acquired the lock -- Unlink current from the cxq or EntryList.
 950   // Normally we'll find current on the EntryList .
 951   // From the perspective of the lock owner (this thread), the
 952   // EntryList is stable and cxq is prepend-only.
 953   // The head of cxq is volatile but the interior is stable.
 954   // In addition, current.TState is stable.
 955 
 956   assert(owner_raw() == current, "invariant");
 957 
 958   UnlinkAfterAcquire(current, &node);
 959   if (_succ == current) _succ = nullptr;
 960 
 961   assert(_succ != current, "invariant");
 962   if (_Responsible == current) {
 963     _Responsible = nullptr;
 964     OrderAccess::fence(); // Dekker pivot-point
 965 
 966     // We may leave threads on cxq|EntryList without a designated
 967     // "Responsible" thread.  This is benign.  When this thread subsequently
 968     // exits the monitor it can "see" such preexisting "old" threads --
 969     // threads that arrived on the cxq|EntryList before the fence, above --
 970     // by LDing cxq|EntryList.  Newly arrived threads -- that is, threads
 971     // that arrive on cxq after the ST:MEMBAR, above -- will set Responsible
 972     // non-null and elect a new "Responsible" timer thread.
 973     //
 974     // This thread executes:
 975     //    ST Responsible=null; MEMBAR    (in enter epilogue - here)
 976     //    LD cxq|EntryList               (in subsequent exit)
 977     //
 978     // Entering threads in the slow/contended path execute:
 979     //    ST cxq=nonnull; MEMBAR; LD Responsible (in enter prolog)
 980     //    The (ST cxq; MEMBAR) is accomplished with CAS().
 981     //
 982     // The MEMBAR, above, prevents the LD of cxq|EntryList in the subsequent
 983     // exit operation from floating above the ST Responsible=null.
 984   }
 985 
 986   // We've acquired ownership with CAS().
 987   // CAS is serializing -- it has MEMBAR/FENCE-equivalent semantics.
 988   // But since the CAS() this thread may have also stored into _succ,
 989   // EntryList, cxq or Responsible.  These meta-data updates must be
 990   // visible __before this thread subsequently drops the lock.
 991   // Consider what could occur if we didn't enforce this constraint --
 992   // STs to monitor meta-data and user-data could reorder with (become
 993   // visible after) the ST in exit that drops ownership of the lock.
 994   // Some other thread could then acquire the lock, but observe inconsistent
 995   // or old monitor meta-data and heap data.  That violates the JMM.
 996   // To that end, the 1-0 exit() operation must have at least STST|LDST
 997   // "release" barrier semantics.  Specifically, there must be at least a
 998   // STST|LDST barrier in exit() before the ST of null into _owner that drops
 999   // the lock.   The barrier ensures that changes to monitor meta-data and data
1000   // protected by the lock will be visible before we release the lock, and
1001   // therefore before some other thread (CPU) has a chance to acquire the lock.
1002   // See also: http://gee.cs.oswego.edu/dl/jmm/cookbook.html.
1003   //
1004   // Critically, any prior STs to _succ or EntryList must be visible before
1005   // the ST of null into _owner in the *subsequent* (following) corresponding
1006   // monitorexit.  Recall too, that in 1-0 mode monitorexit does not necessarily
1007   // execute a serializing instruction.
1008 
1009   return;
1010 }
1011 
1012 // ReenterI() is a specialized inline form of the latter half of the
1013 // contended slow-path from EnterI().  We use ReenterI() only for
1014 // monitor reentry in wait().
1015 //
1016 // In the future we should reconcile EnterI() and ReenterI().
1017 
1018 void ObjectMonitor::ReenterI(JavaThread* current, ObjectWaiter* currentNode) {
1019   assert(current != nullptr, "invariant");
1020   assert(current->thread_state() != _thread_blocked, "invariant");
1021   assert(currentNode != nullptr, "invariant");
1022   assert(currentNode->_thread == current, "invariant");
1023   assert(_waiters > 0, "invariant");
1024   assert_mark_word_consistency();


1025 
1026   for (;;) {
1027     ObjectWaiter::TStates v = currentNode->TState;
1028     guarantee(v == ObjectWaiter::TS_ENTER || v == ObjectWaiter::TS_CXQ, "invariant");
1029     assert(owner_raw() != current, "invariant");
1030 
1031     // This thread has been notified so try to reacquire the lock.
1032     if (TryLock(current) == TryLockResult::Success) {
1033       break;
1034     }
1035 
1036     // If that fails, spin again.  Note that spin count may be zero so the above TryLock
1037     // is necessary.
1038     if (TrySpin(current)) {
1039         break;
1040     }
1041 
1042     {
1043       OSThreadContendState osts(current->osthread());
1044 
1045       assert(current->thread_state() == _thread_in_vm, "invariant");
1046 
1047       {
1048         ClearSuccOnSuspend csos(this);
1049         ThreadBlockInVMPreprocess<ClearSuccOnSuspend> tbivs(current, csos, true /* allow_suspend */);
1050         current->_ParkEvent->park();
1051       }
1052     }
1053 
1054     // Try again, but just so we distinguish between futile wakeups and
1055     // successful wakeups.  The following test isn't algorithmically
1056     // necessary, but it helps us maintain sensible statistics.
1057     if (TryLock(current) == TryLockResult::Success) {
1058       break;
1059     }
1060 
1061     // The lock is still contested.
1062 
1063     // Assuming this is not a spurious wakeup we'll normally
1064     // find that _succ == current.
1065     if (_succ == current) _succ = nullptr;
1066 
1067     // Invariant: after clearing _succ a contending thread
1068     // *must* retry  _owner before parking.
1069     OrderAccess::fence();
1070 
1071     // Keep a tally of the # of futile wakeups.
1072     // Note that the counter is not protected by a lock or updated by atomics.
1073     // That is by design - we trade "lossy" counters which are exposed to
1074     // races during updates for a lower probe effect.
1075     // This PerfData object can be used in parallel with a safepoint.
1076     // See the work around in PerfDataManager::destroy().
1077     OM_PERFDATA_OP(FutileWakeups, inc());
1078   }
1079 
1080   // current has acquired the lock -- Unlink current from the cxq or EntryList .
1081   // Normally we'll find current on the EntryList.
1082   // Unlinking from the EntryList is constant-time and atomic-free.
1083   // From the perspective of the lock owner (this thread), the
1084   // EntryList is stable and cxq is prepend-only.
1085   // The head of cxq is volatile but the interior is stable.
1086   // In addition, current.TState is stable.
1087 
1088   assert(owner_raw() == current, "invariant");
1089   assert_mark_word_consistency();
1090   UnlinkAfterAcquire(current, currentNode);
1091   if (_succ == current) _succ = nullptr;
1092   assert(_succ != current, "invariant");
1093   currentNode->TState = ObjectWaiter::TS_RUN;
1094   OrderAccess::fence();      // see comments at the end of EnterI()
1095 }
1096 
1097 // By convention we unlink a contending thread from EntryList|cxq immediately
1098 // after the thread acquires the lock in ::enter().  Equally, we could defer
1099 // unlinking the thread until ::exit()-time.
1100 
1101 void ObjectMonitor::UnlinkAfterAcquire(JavaThread* current, ObjectWaiter* currentNode) {
1102   assert(owner_raw() == current, "invariant");
1103   assert(currentNode->_thread == current, "invariant");
1104 
1105   if (currentNode->TState == ObjectWaiter::TS_ENTER) {
1106     // Normal case: remove current from the DLL EntryList .
1107     // This is a constant-time operation.
1108     ObjectWaiter* nxt = currentNode->_next;
1109     ObjectWaiter* prv = currentNode->_prev;
1110     if (nxt != nullptr) nxt->_prev = prv;
1111     if (prv != nullptr) prv->_next = nxt;
1112     if (currentNode == _EntryList) _EntryList = nxt;
1113     assert(nxt == nullptr || nxt->TState == ObjectWaiter::TS_ENTER, "invariant");
1114     assert(prv == nullptr || prv->TState == ObjectWaiter::TS_ENTER, "invariant");
1115   } else {
1116     assert(currentNode->TState == ObjectWaiter::TS_CXQ, "invariant");
1117     // Inopportune interleaving -- current is still on the cxq.
1118     // This usually means the enqueue of self raced an exiting thread.
1119     // Normally we'll find current near the front of the cxq, so
1120     // dequeueing is typically fast.  If needbe we can accelerate
1121     // this with some MCS/CHL-like bidirectional list hints and advisory
1122     // back-links so dequeueing from the interior will normally operate
1123     // in constant-time.
1124     // Dequeue current from either the head (with CAS) or from the interior
1125     // with a linear-time scan and normal non-atomic memory operations.
1126     // CONSIDER: if current is on the cxq then simply drain cxq into EntryList
1127     // and then unlink current from EntryList.  We have to drain eventually,
1128     // so it might as well be now.
1129 
1130     ObjectWaiter* v = _cxq;
1131     assert(v != nullptr, "invariant");
1132     if (v != currentNode || Atomic::cmpxchg(&_cxq, v, currentNode->_next) != v) {
1133       // The CAS above can fail from interference IFF a "RAT" arrived.
1134       // In that case current must be in the interior and can no longer be
1135       // at the head of cxq.
1136       if (v == currentNode) {
1137         assert(_cxq != v, "invariant");
1138         v = _cxq;          // CAS above failed - start scan at head of list
1139       }
1140       ObjectWaiter* p;
1141       ObjectWaiter* q = nullptr;
1142       for (p = v; p != nullptr && p != currentNode; p = p->_next) {
1143         q = p;
1144         assert(p->TState == ObjectWaiter::TS_CXQ, "invariant");
1145       }
1146       assert(v != currentNode, "invariant");
1147       assert(p == currentNode, "Node not found on cxq");
1148       assert(p != _cxq, "invariant");
1149       assert(q != nullptr, "invariant");
1150       assert(q->_next == p, "invariant");
1151       q->_next = p->_next;
1152     }
1153   }
1154 
1155 #ifdef ASSERT
1156   // Diagnostic hygiene ...
1157   currentNode->_prev  = (ObjectWaiter*) 0xBAD;
1158   currentNode->_next  = (ObjectWaiter*) 0xBAD;
1159   currentNode->TState = ObjectWaiter::TS_RUN;
1160 #endif
1161 }
1162 
1163 // -----------------------------------------------------------------------------
1164 // Exit support
1165 //
1166 // exit()
1167 // ~~~~~~
1168 // Note that the collector can't reclaim the objectMonitor or deflate
1169 // the object out from underneath the thread calling ::exit() as the
1170 // thread calling ::exit() never transitions to a stable state.
1171 // This inhibits GC, which in turn inhibits asynchronous (and
1172 // inopportune) reclamation of "this".
1173 //
1174 // We'd like to assert that: (THREAD->thread_state() != _thread_blocked) ;
1175 // There's one exception to the claim above, however.  EnterI() can call
1176 // exit() to drop a lock if the acquirer has been externally suspended.
1177 // In that case exit() is called with _thread_state == _thread_blocked,
1178 // but the monitor's _contentions field is > 0, which inhibits reclamation.
1179 //
1180 // 1-0 exit
1181 // ~~~~~~~~
1182 // ::exit() uses a canonical 1-1 idiom with a MEMBAR although some of
1183 // the fast-path operators have been optimized so the common ::exit()
1184 // operation is 1-0, e.g., see macroAssembler_x86.cpp: fast_unlock().
1185 // The code emitted by fast_unlock() elides the usual MEMBAR.  This
1186 // greatly improves latency -- MEMBAR and CAS having considerable local
1187 // latency on modern processors -- but at the cost of "stranding".  Absent the
1188 // MEMBAR, a thread in fast_unlock() can race a thread in the slow
1189 // ::enter() path, resulting in the entering thread being stranding
1190 // and a progress-liveness failure.   Stranding is extremely rare.
1191 // We use timers (timed park operations) & periodic polling to detect
1192 // and recover from stranding.  Potentially stranded threads periodically
1193 // wake up and poll the lock.  See the usage of the _Responsible variable.
1194 //
1195 // The CAS() in enter provides for safety and exclusion, while the CAS or
1196 // MEMBAR in exit provides for progress and avoids stranding.  1-0 locking
1197 // eliminates the CAS/MEMBAR from the exit path, but it admits stranding.
1198 // We detect and recover from stranding with timers.
1199 //
1200 // If a thread transiently strands it'll park until (a) another
1201 // thread acquires the lock and then drops the lock, at which time the
1202 // exiting thread will notice and unpark the stranded thread, or, (b)
1203 // the timer expires.  If the lock is high traffic then the stranding latency
1204 // will be low due to (a).  If the lock is low traffic then the odds of
1205 // stranding are lower, although the worst-case stranding latency
1206 // is longer.  Critically, we don't want to put excessive load in the
1207 // platform's timer subsystem.  We want to minimize both the timer injection
1208 // rate (timers created/sec) as well as the number of timers active at
1209 // any one time.  (more precisely, we want to minimize timer-seconds, which is
1210 // the integral of the # of active timers at any instant over time).
1211 // Both impinge on OS scalability.  Given that, at most one thread parked on
1212 // a monitor will use a timer.
1213 //
1214 // There is also the risk of a futile wake-up. If we drop the lock
1215 // another thread can reacquire the lock immediately, and we can
1216 // then wake a thread unnecessarily. This is benign, and we've
1217 // structured the code so the windows are short and the frequency
1218 // of such futile wakups is low.
1219 
1220 void ObjectMonitor::exit(JavaThread* current, bool not_suspended) {
1221   void* cur = owner_raw();
1222   if (current != cur) {
1223     if (LockingMode != LM_LIGHTWEIGHT && current->is_lock_owned((address)cur)) {
1224       assert(_recursions == 0, "invariant");
1225       set_owner_from_BasicLock(cur, current);  // Convert from BasicLock* to Thread*.
1226       _recursions = 0;
1227     } else {
1228       // Apparent unbalanced locking ...
1229       // Naively we'd like to throw IllegalMonitorStateException.
1230       // As a practical matter we can neither allocate nor throw an
1231       // exception as ::exit() can be called from leaf routines.
1232       // see x86_32.ad Fast_Unlock() and the I1 and I2 properties.
1233       // Upon deeper reflection, however, in a properly run JVM the only
1234       // way we should encounter this situation is in the presence of
1235       // unbalanced JNI locking. TODO: CheckJNICalls.
1236       // See also: CR4414101
1237 #ifdef ASSERT
1238       LogStreamHandle(Error, monitorinflation) lsh;
1239       lsh.print_cr("ERROR: ObjectMonitor::exit(): thread=" INTPTR_FORMAT
1240                     " is exiting an ObjectMonitor it does not own.", p2i(current));
1241       lsh.print_cr("The imbalance is possibly caused by JNI locking.");
1242       print_debug_style_on(&lsh);
1243       assert(false, "Non-balanced monitor enter/exit!");
1244 #endif
1245       return;
1246     }
1247   }
1248 
1249   if (_recursions != 0) {
1250     _recursions--;        // this is simple recursive enter
1251     return;
1252   }
1253 
1254   // Invariant: after setting Responsible=null an thread must execute
1255   // a MEMBAR or other serializing instruction before fetching EntryList|cxq.
1256   _Responsible = nullptr;
1257 
1258 #if INCLUDE_JFR
1259   // get the owner's thread id for the MonitorEnter event
1260   // if it is enabled and the thread isn't suspended
1261   if (not_suspended && EventJavaMonitorEnter::is_enabled()) {
1262     _previous_owner_tid = JFR_THREAD_ID(current);
1263   }
1264 #endif
1265 
1266   for (;;) {
1267     assert(current == owner_raw(), "invariant");
1268 
1269     // Drop the lock.
1270     // release semantics: prior loads and stores from within the critical section
1271     // must not float (reorder) past the following store that drops the lock.
1272     // Uses a storeload to separate release_store(owner) from the
1273     // successor check. The try_set_owner() below uses cmpxchg() so
1274     // we get the fence down there.
1275     release_clear_owner(current);
1276     OrderAccess::storeload();
1277 
1278     if ((intptr_t(_EntryList)|intptr_t(_cxq)) == 0 || _succ != nullptr) {
1279       return;
1280     }
1281     // Other threads are blocked trying to acquire the lock.
1282 
1283     // Normally the exiting thread is responsible for ensuring succession,
1284     // but if other successors are ready or other entering threads are spinning
1285     // then this thread can simply store null into _owner and exit without
1286     // waking a successor.  The existence of spinners or ready successors
1287     // guarantees proper succession (liveness).  Responsibility passes to the
1288     // ready or running successors.  The exiting thread delegates the duty.
1289     // More precisely, if a successor already exists this thread is absolved
1290     // of the responsibility of waking (unparking) one.
1291     //
1292     // The _succ variable is critical to reducing futile wakeup frequency.
1293     // _succ identifies the "heir presumptive" thread that has been made
1294     // ready (unparked) but that has not yet run.  We need only one such
1295     // successor thread to guarantee progress.
1296     // See http://www.usenix.org/events/jvm01/full_papers/dice/dice.pdf
1297     // section 3.3 "Futile Wakeup Throttling" for details.
1298     //
1299     // Note that spinners in Enter() also set _succ non-null.
1300     // In the current implementation spinners opportunistically set
1301     // _succ so that exiting threads might avoid waking a successor.
1302     // Another less appealing alternative would be for the exiting thread
1303     // to drop the lock and then spin briefly to see if a spinner managed
1304     // to acquire the lock.  If so, the exiting thread could exit
1305     // immediately without waking a successor, otherwise the exiting
1306     // thread would need to dequeue and wake a successor.
1307     // (Note that we'd need to make the post-drop spin short, but no
1308     // shorter than the worst-case round-trip cache-line migration time.
1309     // The dropped lock needs to become visible to the spinner, and then
1310     // the acquisition of the lock by the spinner must become visible to
1311     // the exiting thread).
1312 
1313     // It appears that an heir-presumptive (successor) must be made ready.
1314     // Only the current lock owner can manipulate the EntryList or
1315     // drain _cxq, so we need to reacquire the lock.  If we fail
1316     // to reacquire the lock the responsibility for ensuring succession
1317     // falls to the new owner.
1318     //
1319     if (try_set_owner_from(nullptr, current) != nullptr) {
1320       return;
1321     }
1322 
1323     guarantee(owner_raw() == current, "invariant");
1324 
1325     ObjectWaiter* w = nullptr;
1326 
1327     w = _EntryList;
1328     if (w != nullptr) {
1329       // I'd like to write: guarantee (w->_thread != current).
1330       // But in practice an exiting thread may find itself on the EntryList.
1331       // Let's say thread T1 calls O.wait().  Wait() enqueues T1 on O's waitset and
1332       // then calls exit().  Exit release the lock by setting O._owner to null.
1333       // Let's say T1 then stalls.  T2 acquires O and calls O.notify().  The
1334       // notify() operation moves T1 from O's waitset to O's EntryList. T2 then
1335       // release the lock "O".  T2 resumes immediately after the ST of null into
1336       // _owner, above.  T2 notices that the EntryList is populated, so it
1337       // reacquires the lock and then finds itself on the EntryList.
1338       // Given all that, we have to tolerate the circumstance where "w" is
1339       // associated with current.
1340       assert(w->TState == ObjectWaiter::TS_ENTER, "invariant");
1341       ExitEpilog(current, w);
1342       return;
1343     }
1344 
1345     // If we find that both _cxq and EntryList are null then just
1346     // re-run the exit protocol from the top.
1347     w = _cxq;
1348     if (w == nullptr) continue;
1349 
1350     // Drain _cxq into EntryList - bulk transfer.
1351     // First, detach _cxq.
1352     // The following loop is tantamount to: w = swap(&cxq, nullptr)
1353     for (;;) {
1354       assert(w != nullptr, "Invariant");
1355       ObjectWaiter* u = Atomic::cmpxchg(&_cxq, w, (ObjectWaiter*)nullptr);
1356       if (u == w) break;
1357       w = u;
1358     }
1359 
1360     assert(w != nullptr, "invariant");
1361     assert(_EntryList == nullptr, "invariant");
1362 
1363     // Convert the LIFO SLL anchored by _cxq into a DLL.
1364     // The list reorganization step operates in O(LENGTH(w)) time.
1365     // It's critical that this step operate quickly as
1366     // "current" still holds the outer-lock, restricting parallelism
1367     // and effectively lengthening the critical section.
1368     // Invariant: s chases t chases u.
1369     // TODO-FIXME: consider changing EntryList from a DLL to a CDLL so
1370     // we have faster access to the tail.
1371 
1372     _EntryList = w;
1373     ObjectWaiter* q = nullptr;
1374     ObjectWaiter* p;
1375     for (p = w; p != nullptr; p = p->_next) {
1376       guarantee(p->TState == ObjectWaiter::TS_CXQ, "Invariant");
1377       p->TState = ObjectWaiter::TS_ENTER;
1378       p->_prev = q;
1379       q = p;
1380     }
1381 
1382     // In 1-0 mode we need: ST EntryList; MEMBAR #storestore; ST _owner = nullptr
1383     // The MEMBAR is satisfied by the release_store() operation in ExitEpilog().
1384 
1385     // See if we can abdicate to a spinner instead of waking a thread.
1386     // A primary goal of the implementation is to reduce the
1387     // context-switch rate.
1388     if (_succ != nullptr) continue;
1389 
1390     w = _EntryList;
1391     if (w != nullptr) {
1392       guarantee(w->TState == ObjectWaiter::TS_ENTER, "invariant");
1393       ExitEpilog(current, w);
1394       return;
1395     }
1396   }
1397 }
1398 
1399 void ObjectMonitor::ExitEpilog(JavaThread* current, ObjectWaiter* Wakee) {
1400   assert(owner_raw() == current, "invariant");
1401 
1402   // Exit protocol:
1403   // 1. ST _succ = wakee
1404   // 2. membar #loadstore|#storestore;
1405   // 2. ST _owner = nullptr
1406   // 3. unpark(wakee)
1407 
1408   _succ = Wakee->_thread;
1409   ParkEvent * Trigger = Wakee->_event;
1410 
1411   // Hygiene -- once we've set _owner = nullptr we can't safely dereference Wakee again.
1412   // The thread associated with Wakee may have grabbed the lock and "Wakee" may be
1413   // out-of-scope (non-extant).
1414   Wakee  = nullptr;
1415 
1416   // Drop the lock.
1417   // Uses a fence to separate release_store(owner) from the LD in unpark().
1418   release_clear_owner(current);
1419   OrderAccess::fence();
1420 
1421   DTRACE_MONITOR_PROBE(contended__exit, this, object(), current);
1422   Trigger->unpark();
1423 
1424   // Maintain stats and report events to JVMTI
1425   OM_PERFDATA_OP(Parks, inc());
1426 }
1427 
1428 // complete_exit exits a lock returning recursion count
1429 // complete_exit requires an inflated monitor
1430 // The _owner field is not always the Thread addr even with an
1431 // inflated monitor, e.g. the monitor can be inflated by a non-owning
1432 // thread due to contention.
1433 intx ObjectMonitor::complete_exit(JavaThread* current) {
1434   assert(InitDone, "Unexpectedly not initialized");
1435 
1436   void* cur = owner_raw();
1437   if (current != cur) {
1438     if (LockingMode != LM_LIGHTWEIGHT && current->is_lock_owned((address)cur)) {
1439       assert(_recursions == 0, "internal state error");
1440       set_owner_from_BasicLock(cur, current);  // Convert from BasicLock* to Thread*.
1441       _recursions = 0;
1442     }
1443   }
1444 
1445   guarantee(current == owner_raw(), "complete_exit not owner");
1446   intx save = _recursions; // record the old recursion count
1447   _recursions = 0;         // set the recursion level to be 0
1448   exit(current);           // exit the monitor
1449   guarantee(owner_raw() != current, "invariant");
1450   return save;
1451 }
1452 
1453 // Checks that the current THREAD owns this monitor and causes an
1454 // immediate return if it doesn't. We don't use the CHECK macro
1455 // because we want the IMSE to be the only exception that is thrown
1456 // from the call site when false is returned. Any other pending
1457 // exception is ignored.
1458 #define CHECK_OWNER()                                                  \
1459   do {                                                                 \
1460     if (!check_owner(THREAD)) {                                        \
1461        assert(HAS_PENDING_EXCEPTION, "expected a pending IMSE here."); \
1462        return;                                                         \
1463      }                                                                 \
1464   } while (false)
1465 
1466 // Returns true if the specified thread owns the ObjectMonitor.
1467 // Otherwise returns false and throws IllegalMonitorStateException
1468 // (IMSE). If there is a pending exception and the specified thread
1469 // is not the owner, that exception will be replaced by the IMSE.
1470 bool ObjectMonitor::check_owner(TRAPS) {
1471   JavaThread* current = THREAD;
1472   void* cur = owner_raw();
1473   assert(cur != anon_owner_ptr(), "no anon owner here");
1474   if (cur == current) {
1475     return true;
1476   }
1477   if (LockingMode != LM_LIGHTWEIGHT && current->is_lock_owned((address)cur)) {
1478     set_owner_from_BasicLock(cur, current);  // Convert from BasicLock* to Thread*.
1479     _recursions = 0;
1480     return true;
1481   }
1482   THROW_MSG_(vmSymbols::java_lang_IllegalMonitorStateException(),
1483              "current thread is not owner", false);
1484 }
1485 
1486 static inline bool is_excluded(const Klass* monitor_klass) {
1487   assert(monitor_klass != nullptr, "invariant");
1488   NOT_JFR_RETURN_(false);
1489   JFR_ONLY(return vmSymbols::jdk_jfr_internal_HiddenWait() == monitor_klass->name();)
1490 }
1491 
1492 static void post_monitor_wait_event(EventJavaMonitorWait* event,
1493                                     ObjectMonitor* monitor,
1494                                     uint64_t notifier_tid,
1495                                     jlong timeout,
1496                                     bool timedout) {
1497   assert(event != nullptr, "invariant");
1498   assert(monitor != nullptr, "invariant");
1499   const Klass* monitor_klass = monitor->object()->klass();
1500   if (is_excluded(monitor_klass)) {
1501     return;
1502   }
1503   event->set_monitorClass(monitor_klass);
1504   event->set_timeout(timeout);
1505   // Set an address that is 'unique enough', such that events close in
1506   // time and with the same address are likely (but not guaranteed) to
1507   // belong to the same object.
1508   event->set_address((uintptr_t)monitor);
1509   event->set_notifier(notifier_tid);
1510   event->set_timedOut(timedout);
1511   event->commit();
1512 }
1513 
1514 // -----------------------------------------------------------------------------
1515 // Wait/Notify/NotifyAll
1516 //
1517 // Note: a subset of changes to ObjectMonitor::wait()
1518 // will need to be replicated in complete_exit
1519 void ObjectMonitor::wait(jlong millis, bool interruptible, TRAPS) {
1520   JavaThread* current = THREAD;
1521 
1522   assert(InitDone, "Unexpectedly not initialized");
1523 
1524   CHECK_OWNER();  // Throws IMSE if not owner.
1525 
1526   EventJavaMonitorWait event;
1527 
1528   // check for a pending interrupt
1529   if (interruptible && current->is_interrupted(true) && !HAS_PENDING_EXCEPTION) {
1530     // post monitor waited event.  Note that this is past-tense, we are done waiting.
1531     if (JvmtiExport::should_post_monitor_waited()) {
1532       // Note: 'false' parameter is passed here because the
1533       // wait was not timed out due to thread interrupt.
1534       JvmtiExport::post_monitor_waited(current, this, false);
1535 
1536       // In this short circuit of the monitor wait protocol, the
1537       // current thread never drops ownership of the monitor and
1538       // never gets added to the wait queue so the current thread
1539       // cannot be made the successor. This means that the
1540       // JVMTI_EVENT_MONITOR_WAITED event handler cannot accidentally
1541       // consume an unpark() meant for the ParkEvent associated with
1542       // this ObjectMonitor.
1543     }
1544     if (event.should_commit()) {
1545       post_monitor_wait_event(&event, this, 0, millis, false);
1546     }
1547     THROW(vmSymbols::java_lang_InterruptedException());
1548     return;
1549   }
1550 
1551   current->set_current_waiting_monitor(this);
1552 
1553   // create a node to be put into the queue
1554   // Critically, after we reset() the event but prior to park(), we must check
1555   // for a pending interrupt.
1556   ObjectWaiter node(current);
1557   node.TState = ObjectWaiter::TS_WAIT;
1558   current->_ParkEvent->reset();
1559   OrderAccess::fence();          // ST into Event; membar ; LD interrupted-flag
1560 
1561   // Enter the waiting queue, which is a circular doubly linked list in this case
1562   // but it could be a priority queue or any data structure.
1563   // _WaitSetLock protects the wait queue.  Normally the wait queue is accessed only
1564   // by the owner of the monitor *except* in the case where park()
1565   // returns because of a timeout of interrupt.  Contention is exceptionally rare
1566   // so we use a simple spin-lock instead of a heavier-weight blocking lock.
1567 
1568   Thread::SpinAcquire(&_WaitSetLock, "WaitSet - add");
1569   AddWaiter(&node);
1570   Thread::SpinRelease(&_WaitSetLock);
1571 
1572   _Responsible = nullptr;
1573 
1574   intx save = _recursions;     // record the old recursion count
1575   _waiters++;                  // increment the number of waiters
1576   _recursions = 0;             // set the recursion level to be 1
1577   exit(current);               // exit the monitor
1578   guarantee(owner_raw() != current, "invariant");
1579 
1580   // The thread is on the WaitSet list - now park() it.
1581   // On MP systems it's conceivable that a brief spin before we park
1582   // could be profitable.
1583   //
1584   // TODO-FIXME: change the following logic to a loop of the form
1585   //   while (!timeout && !interrupted && _notified == 0) park()
1586 
1587   int ret = OS_OK;
1588   int WasNotified = 0;
1589 
1590   // Need to check interrupt state whilst still _thread_in_vm
1591   bool interrupted = interruptible && current->is_interrupted(false);
1592 
1593   { // State transition wrappers
1594     OSThread* osthread = current->osthread();
1595     OSThreadWaitState osts(osthread, true);
1596 
1597     assert(current->thread_state() == _thread_in_vm, "invariant");
1598 
1599     {
1600       ClearSuccOnSuspend csos(this);
1601       ThreadBlockInVMPreprocess<ClearSuccOnSuspend> tbivs(current, csos, true /* allow_suspend */);
1602       if (interrupted || HAS_PENDING_EXCEPTION) {
1603         // Intentionally empty
1604       } else if (node._notified == 0) {
1605         if (millis <= 0) {
1606           current->_ParkEvent->park();
1607         } else {
1608           ret = current->_ParkEvent->park(millis);
1609         }
1610       }
1611     }
1612 
1613     // Node may be on the WaitSet, the EntryList (or cxq), or in transition
1614     // from the WaitSet to the EntryList.
1615     // See if we need to remove Node from the WaitSet.
1616     // We use double-checked locking to avoid grabbing _WaitSetLock
1617     // if the thread is not on the wait queue.
1618     //
1619     // Note that we don't need a fence before the fetch of TState.
1620     // In the worst case we'll fetch a old-stale value of TS_WAIT previously
1621     // written by the is thread. (perhaps the fetch might even be satisfied
1622     // by a look-aside into the processor's own store buffer, although given
1623     // the length of the code path between the prior ST and this load that's
1624     // highly unlikely).  If the following LD fetches a stale TS_WAIT value
1625     // then we'll acquire the lock and then re-fetch a fresh TState value.
1626     // That is, we fail toward safety.
1627 
1628     if (node.TState == ObjectWaiter::TS_WAIT) {
1629       Thread::SpinAcquire(&_WaitSetLock, "WaitSet - unlink");
1630       if (node.TState == ObjectWaiter::TS_WAIT) {
1631         DequeueSpecificWaiter(&node);       // unlink from WaitSet
1632         assert(node._notified == 0, "invariant");
1633         node.TState = ObjectWaiter::TS_RUN;
1634       }
1635       Thread::SpinRelease(&_WaitSetLock);
1636     }
1637 
1638     // The thread is now either on off-list (TS_RUN),
1639     // on the EntryList (TS_ENTER), or on the cxq (TS_CXQ).
1640     // The Node's TState variable is stable from the perspective of this thread.
1641     // No other threads will asynchronously modify TState.
1642     guarantee(node.TState != ObjectWaiter::TS_WAIT, "invariant");
1643     OrderAccess::loadload();
1644     if (_succ == current) _succ = nullptr;
1645     WasNotified = node._notified;
1646 
1647     // Reentry phase -- reacquire the monitor.
1648     // re-enter contended monitor after object.wait().
1649     // retain OBJECT_WAIT state until re-enter successfully completes
1650     // Thread state is thread_in_vm and oop access is again safe,
1651     // although the raw address of the object may have changed.
1652     // (Don't cache naked oops over safepoints, of course).
1653 
1654     // post monitor waited event. Note that this is past-tense, we are done waiting.
1655     if (JvmtiExport::should_post_monitor_waited()) {
1656       JvmtiExport::post_monitor_waited(current, this, ret == OS_TIMEOUT);
1657 
1658       if (node._notified != 0 && _succ == current) {
1659         // In this part of the monitor wait-notify-reenter protocol it
1660         // is possible (and normal) for another thread to do a fastpath
1661         // monitor enter-exit while this thread is still trying to get
1662         // to the reenter portion of the protocol.
1663         //
1664         // The ObjectMonitor was notified and the current thread is
1665         // the successor which also means that an unpark() has already
1666         // been done. The JVMTI_EVENT_MONITOR_WAITED event handler can
1667         // consume the unpark() that was done when the successor was
1668         // set because the same ParkEvent is shared between Java
1669         // monitors and JVM/TI RawMonitors (for now).
1670         //
1671         // We redo the unpark() to ensure forward progress, i.e., we
1672         // don't want all pending threads hanging (parked) with none
1673         // entering the unlocked monitor.
1674         node._event->unpark();
1675       }
1676     }
1677 
1678     if (event.should_commit()) {
1679       post_monitor_wait_event(&event, this, node._notifier_tid, millis, ret == OS_TIMEOUT);
1680     }
1681 
1682     OrderAccess::fence();
1683 
1684     assert(owner_raw() != current, "invariant");
1685     ObjectWaiter::TStates v = node.TState;
1686     if (v == ObjectWaiter::TS_RUN) {
1687       enter(current);
1688     } else {
1689       guarantee(v == ObjectWaiter::TS_ENTER || v == ObjectWaiter::TS_CXQ, "invariant");
1690       ReenterI(current, &node);
1691       node.wait_reenter_end(this);
1692     }
1693 
1694     // current has reacquired the lock.
1695     // Lifecycle - the node representing current must not appear on any queues.
1696     // Node is about to go out-of-scope, but even if it were immortal we wouldn't
1697     // want residual elements associated with this thread left on any lists.
1698     guarantee(node.TState == ObjectWaiter::TS_RUN, "invariant");
1699     assert(owner_raw() == current, "invariant");
1700     assert(_succ != current, "invariant");
1701   } // OSThreadWaitState()
1702 
1703   current->set_current_waiting_monitor(nullptr);
1704 
1705   guarantee(_recursions == 0, "invariant");
1706   int relock_count = JvmtiDeferredUpdates::get_and_reset_relock_count_after_wait(current);
1707   _recursions =   save          // restore the old recursion count
1708                 + relock_count; //  increased by the deferred relock count
1709   current->inc_held_monitor_count(relock_count); // Deopt never entered these counts.
1710   _waiters--;             // decrement the number of waiters
1711 
1712   // Verify a few postconditions
1713   assert(owner_raw() == current, "invariant");
1714   assert(_succ != current, "invariant");
1715   assert_mark_word_consistency();
1716 
1717   // check if the notification happened
1718   if (!WasNotified) {
1719     // no, it could be timeout or Thread.interrupt() or both
1720     // check for interrupt event, otherwise it is timeout
1721     if (interruptible && current->is_interrupted(true) && !HAS_PENDING_EXCEPTION) {
1722       THROW(vmSymbols::java_lang_InterruptedException());
1723     }
1724   }
1725 
1726   // NOTE: Spurious wake up will be consider as timeout.
1727   // Monitor notify has precedence over thread interrupt.
1728 }
1729 
1730 
1731 // Consider:
1732 // If the lock is cool (cxq == null && succ == null) and we're on an MP system
1733 // then instead of transferring a thread from the WaitSet to the EntryList
1734 // we might just dequeue a thread from the WaitSet and directly unpark() it.
1735 
1736 void ObjectMonitor::INotify(JavaThread* current) {
1737   Thread::SpinAcquire(&_WaitSetLock, "WaitSet - notify");
1738   ObjectWaiter* iterator = DequeueWaiter();
1739   if (iterator != nullptr) {
1740     guarantee(iterator->TState == ObjectWaiter::TS_WAIT, "invariant");
1741     guarantee(iterator->_notified == 0, "invariant");
1742     // Disposition - what might we do with iterator ?
1743     // a.  add it directly to the EntryList - either tail (policy == 1)
1744     //     or head (policy == 0).
1745     // b.  push it onto the front of the _cxq (policy == 2).
1746     // For now we use (b).
1747 
1748     iterator->TState = ObjectWaiter::TS_ENTER;
1749 
1750     iterator->_notified = 1;
1751     iterator->_notifier_tid = JFR_THREAD_ID(current);
1752 
1753     ObjectWaiter* list = _EntryList;
1754     if (list != nullptr) {
1755       assert(list->_prev == nullptr, "invariant");
1756       assert(list->TState == ObjectWaiter::TS_ENTER, "invariant");
1757       assert(list != iterator, "invariant");
1758     }
1759 
1760     // prepend to cxq
1761     if (list == nullptr) {
1762       iterator->_next = iterator->_prev = nullptr;
1763       _EntryList = iterator;
1764     } else {
1765       iterator->TState = ObjectWaiter::TS_CXQ;
1766       for (;;) {
1767         ObjectWaiter* front = _cxq;
1768         iterator->_next = front;
1769         if (Atomic::cmpxchg(&_cxq, front, iterator) == front) {
1770           break;
1771         }
1772       }
1773     }
1774 
1775     // _WaitSetLock protects the wait queue, not the EntryList.  We could
1776     // move the add-to-EntryList operation, above, outside the critical section
1777     // protected by _WaitSetLock.  In practice that's not useful.  With the
1778     // exception of  wait() timeouts and interrupts the monitor owner
1779     // is the only thread that grabs _WaitSetLock.  There's almost no contention
1780     // on _WaitSetLock so it's not profitable to reduce the length of the
1781     // critical section.
1782 
1783     iterator->wait_reenter_begin(this);
1784   }
1785   Thread::SpinRelease(&_WaitSetLock);
1786 }
1787 
1788 // Consider: a not-uncommon synchronization bug is to use notify() when
1789 // notifyAll() is more appropriate, potentially resulting in stranded
1790 // threads; this is one example of a lost wakeup. A useful diagnostic
1791 // option is to force all notify() operations to behave as notifyAll().
1792 //
1793 // Note: We can also detect many such problems with a "minimum wait".
1794 // When the "minimum wait" is set to a small non-zero timeout value
1795 // and the program does not hang whereas it did absent "minimum wait",
1796 // that suggests a lost wakeup bug.
1797 
1798 void ObjectMonitor::notify(TRAPS) {
1799   JavaThread* current = THREAD;
1800   CHECK_OWNER();  // Throws IMSE if not owner.
1801   if (_WaitSet == nullptr) {
1802     return;
1803   }
1804   DTRACE_MONITOR_PROBE(notify, this, object(), current);
1805   INotify(current);
1806   OM_PERFDATA_OP(Notifications, inc(1));
1807 }
1808 
1809 
1810 // The current implementation of notifyAll() transfers the waiters one-at-a-time
1811 // from the waitset to the EntryList. This could be done more efficiently with a
1812 // single bulk transfer but in practice it's not time-critical. Beware too,
1813 // that in prepend-mode we invert the order of the waiters. Let's say that the
1814 // waitset is "ABCD" and the EntryList is "XYZ". After a notifyAll() in prepend
1815 // mode the waitset will be empty and the EntryList will be "DCBAXYZ".
1816 
1817 void ObjectMonitor::notifyAll(TRAPS) {
1818   JavaThread* current = THREAD;
1819   CHECK_OWNER();  // Throws IMSE if not owner.
1820   if (_WaitSet == nullptr) {
1821     return;
1822   }
1823 
1824   DTRACE_MONITOR_PROBE(notifyAll, this, object(), current);
1825   int tally = 0;
1826   while (_WaitSet != nullptr) {
1827     tally++;
1828     INotify(current);
1829   }
1830 
1831   OM_PERFDATA_OP(Notifications, inc(tally));
1832 }
1833 
1834 // -----------------------------------------------------------------------------
1835 // Adaptive Spinning Support
1836 //
1837 // Adaptive spin-then-block - rational spinning
1838 //
1839 // Note that we spin "globally" on _owner with a classic SMP-polite TATAS
1840 // algorithm.  On high order SMP systems it would be better to start with
1841 // a brief global spin and then revert to spinning locally.  In the spirit of MCS/CLH,
1842 // a contending thread could enqueue itself on the cxq and then spin locally
1843 // on a thread-specific variable such as its ParkEvent._Event flag.
1844 // That's left as an exercise for the reader.  Note that global spinning is
1845 // not problematic on Niagara, as the L2 cache serves the interconnect and
1846 // has both low latency and massive bandwidth.
1847 //
1848 // Broadly, we can fix the spin frequency -- that is, the % of contended lock
1849 // acquisition attempts where we opt to spin --  at 100% and vary the spin count
1850 // (duration) or we can fix the count at approximately the duration of
1851 // a context switch and vary the frequency.   Of course we could also
1852 // vary both satisfying K == Frequency * Duration, where K is adaptive by monitor.
1853 // For a description of 'Adaptive spin-then-block mutual exclusion in
1854 // multi-threaded processing,' see U.S. Pat. No. 8046758.
1855 //
1856 // This implementation varies the duration "D", where D varies with
1857 // the success rate of recent spin attempts. (D is capped at approximately
1858 // length of a round-trip context switch).  The success rate for recent
1859 // spin attempts is a good predictor of the success rate of future spin
1860 // attempts.  The mechanism adapts automatically to varying critical
1861 // section length (lock modality), system load and degree of parallelism.
1862 // D is maintained per-monitor in _SpinDuration and is initialized
1863 // optimistically.  Spin frequency is fixed at 100%.
1864 //
1865 // Note that _SpinDuration is volatile, but we update it without locks
1866 // or atomics.  The code is designed so that _SpinDuration stays within
1867 // a reasonable range even in the presence of races.  The arithmetic
1868 // operations on _SpinDuration are closed over the domain of legal values,
1869 // so at worst a race will install and older but still legal value.
1870 // At the very worst this introduces some apparent non-determinism.
1871 // We might spin when we shouldn't or vice-versa, but since the spin
1872 // count are relatively short, even in the worst case, the effect is harmless.
1873 //
1874 // Care must be taken that a low "D" value does not become an
1875 // an absorbing state.  Transient spinning failures -- when spinning
1876 // is overall profitable -- should not cause the system to converge
1877 // on low "D" values.  We want spinning to be stable and predictable
1878 // and fairly responsive to change and at the same time we don't want
1879 // it to oscillate, become metastable, be "too" non-deterministic,
1880 // or converge on or enter undesirable stable absorbing states.
1881 //
1882 // We implement a feedback-based control system -- using past behavior
1883 // to predict future behavior.  We face two issues: (a) if the
1884 // input signal is random then the spin predictor won't provide optimal
1885 // results, and (b) if the signal frequency is too high then the control
1886 // system, which has some natural response lag, will "chase" the signal.
1887 // (b) can arise from multimodal lock hold times.  Transient preemption
1888 // can also result in apparent bimodal lock hold times.
1889 // Although sub-optimal, neither condition is particularly harmful, as
1890 // in the worst-case we'll spin when we shouldn't or vice-versa.
1891 // The maximum spin duration is rather short so the failure modes aren't bad.
1892 // To be conservative, I've tuned the gain in system to bias toward
1893 // _not spinning.  Relatedly, the system can sometimes enter a mode where it
1894 // "rings" or oscillates between spinning and not spinning.  This happens
1895 // when spinning is just on the cusp of profitability, however, so the
1896 // situation is not dire.  The state is benign -- there's no need to add
1897 // hysteresis control to damp the transition rate between spinning and
1898 // not spinning.
1899 
1900 int ObjectMonitor::Knob_SpinLimit    = 5000;   // derived by an external tool
1901 
1902 static int Knob_Bonus               = 100;     // spin success bonus
1903 static int Knob_Penalty             = 200;     // spin failure penalty
1904 static int Knob_Poverty             = 1000;
1905 static int Knob_FixedSpin           = 0;
1906 static int Knob_PreSpin             = 10;      // 20-100 likely better, but it's not better in my testing.
1907 
1908 inline static int adjust_up(int spin_duration) {
1909   int x = spin_duration;
1910   if (x < ObjectMonitor::Knob_SpinLimit) {
1911     if (x < Knob_Poverty) {
1912       x = Knob_Poverty;
1913     }
1914     return x + Knob_Bonus;
1915   } else {
1916     return spin_duration;
1917   }
1918 }
1919 
1920 inline static int adjust_down(int spin_duration) {
1921   // TODO: Use an AIMD-like policy to adjust _SpinDuration.
1922   // AIMD is globally stable.
1923   int x = spin_duration;
1924   if (x > 0) {
1925     // Consider an AIMD scheme like: x -= (x >> 3) + 100
1926     // This is globally sample and tends to damp the response.
1927     x -= Knob_Penalty;
1928     if (x < 0) { x = 0; }
1929     return x;
1930   } else {
1931     return spin_duration;
1932   }
1933 }
1934 
1935 bool ObjectMonitor::short_fixed_spin(JavaThread* current, int spin_count, bool adapt) {
1936   for (int ctr = 0; ctr < spin_count; ctr++) {
1937     TryLockResult status = TryLock(current);
1938     if (status == TryLockResult::Success) {
1939       if (adapt) {
1940         _SpinDuration = adjust_up(_SpinDuration);
1941       }
1942       return true;
1943     } else if (status == TryLockResult::Interference) {
1944       break;
1945     }
1946     SpinPause();
1947   }
1948   return false;
1949 }
1950 
1951 // Spinning: Fixed frequency (100%), vary duration
1952 bool ObjectMonitor::TrySpin(JavaThread* current) {
1953 
1954   // Dumb, brutal spin.  Good for comparative measurements against adaptive spinning.
1955   int knob_fixed_spin = Knob_FixedSpin;  // 0 (don't spin: default), 2000 good test
1956   if (knob_fixed_spin > 0) {
1957     return short_fixed_spin(current, knob_fixed_spin, false);
1958   }
1959 
1960   // Admission control - verify preconditions for spinning
1961   //
1962   // We always spin a little bit, just to prevent _SpinDuration == 0 from
1963   // becoming an absorbing state.  Put another way, we spin briefly to
1964   // sample, just in case the system load, parallelism, contention, or lock
1965   // modality changed.
1966 
1967   int knob_pre_spin = Knob_PreSpin; // 10 (default), 100, 1000 or 2000
1968   if (short_fixed_spin(current, knob_pre_spin, true)) {
1969     return true;
1970   }
1971 
1972   //
1973   // Consider the following alternative:
1974   // Periodically set _SpinDuration = _SpinLimit and try a long/full
1975   // spin attempt.  "Periodically" might mean after a tally of
1976   // the # of failed spin attempts (or iterations) reaches some threshold.
1977   // This takes us into the realm of 1-out-of-N spinning, where we
1978   // hold the duration constant but vary the frequency.
1979 
1980   int ctr = _SpinDuration;
1981   if (ctr <= 0) return false;
1982 
1983   // We're good to spin ... spin ingress.
1984   // CONSIDER: use Prefetch::write() to avoid RTS->RTO upgrades
1985   // when preparing to LD...CAS _owner, etc and the CAS is likely
1986   // to succeed.
1987   if (_succ == nullptr) {
1988     _succ = current;
1989   }
1990   Thread* prv = nullptr;
1991 
1992   // There are three ways to exit the following loop:
1993   // 1.  A successful spin where this thread has acquired the lock.
1994   // 2.  Spin failure with prejudice
1995   // 3.  Spin failure without prejudice
1996 
1997   while (--ctr >= 0) {
1998 
1999     // Periodic polling -- Check for pending GC
2000     // Threads may spin while they're unsafe.
2001     // We don't want spinning threads to delay the JVM from reaching
2002     // a stop-the-world safepoint or to steal cycles from GC.
2003     // If we detect a pending safepoint we abort in order that
2004     // (a) this thread, if unsafe, doesn't delay the safepoint, and (b)
2005     // this thread, if safe, doesn't steal cycles from GC.
2006     // This is in keeping with the "no loitering in runtime" rule.
2007     // We periodically check to see if there's a safepoint pending.
2008     if ((ctr & 0xFF) == 0) {
2009       // Can't call SafepointMechanism::should_process() since that
2010       // might update the poll values and we could be in a thread_blocked
2011       // state here which is not allowed so just check the poll.
2012       if (SafepointMechanism::local_poll_armed(current)) {
2013         break;
2014       }
2015       SpinPause();
2016     }
2017 
2018     // Probe _owner with TATAS
2019     // If this thread observes the monitor transition or flicker
2020     // from locked to unlocked to locked, then the odds that this
2021     // thread will acquire the lock in this spin attempt go down
2022     // considerably.  The same argument applies if the CAS fails
2023     // or if we observe _owner change from one non-null value to
2024     // another non-null value.   In such cases we might abort
2025     // the spin without prejudice or apply a "penalty" to the
2026     // spin count-down variable "ctr", reducing it by 100, say.
2027 
2028     JavaThread* ox = static_cast<JavaThread*>(owner_raw());
2029     if (ox == nullptr) {
2030       ox = static_cast<JavaThread*>(try_set_owner_from(nullptr, current));
2031       if (ox == nullptr) {
2032         // The CAS succeeded -- this thread acquired ownership
2033         // Take care of some bookkeeping to exit spin state.
2034         if (_succ == current) {
2035           _succ = nullptr;
2036         }
2037 
2038         // Increase _SpinDuration :
2039         // The spin was successful (profitable) so we tend toward
2040         // longer spin attempts in the future.
2041         // CONSIDER: factor "ctr" into the _SpinDuration adjustment.
2042         // If we acquired the lock early in the spin cycle it
2043         // makes sense to increase _SpinDuration proportionally.
2044         // Note that we don't clamp SpinDuration precisely at SpinLimit.
2045         _SpinDuration = adjust_up(_SpinDuration);
2046         return true;
2047       }
2048 
2049       // The CAS failed ... we can take any of the following actions:
2050       // * penalize: ctr -= CASPenalty
2051       // * exit spin with prejudice -- abort without adapting spinner
2052       // * exit spin without prejudice.
2053       // * Since CAS is high-latency, retry again immediately.
2054       break;
2055     }
2056 
2057     // Did lock ownership change hands ?
2058     if (ox != prv && prv != nullptr) {
2059       break;
2060     }
2061     prv = ox;
2062 
2063     if (_succ == nullptr) {
2064       _succ = current;
2065     }
2066   }
2067 
2068   // Spin failed with prejudice -- reduce _SpinDuration.
2069   if (ctr < 0) {
2070     _SpinDuration = adjust_down(_SpinDuration);
2071   }
2072 
2073   if (_succ == current) {
2074     _succ = nullptr;
2075     // Invariant: after setting succ=null a contending thread
2076     // must recheck-retry _owner before parking.  This usually happens
2077     // in the normal usage of TrySpin(), but it's safest
2078     // to make TrySpin() as foolproof as possible.
2079     OrderAccess::fence();
2080     if (TryLock(current) == TryLockResult::Success) {
2081       return true;
2082     }
2083   }
2084 
2085   return false;
2086 }
2087 
2088 
2089 // -----------------------------------------------------------------------------
2090 // WaitSet management ...
2091 
2092 ObjectWaiter::ObjectWaiter(JavaThread* current) {
2093   _next     = nullptr;
2094   _prev     = nullptr;
2095   _notified = 0;
2096   _notifier_tid = 0;
2097   TState    = TS_RUN;
2098   _thread   = current;
2099   _event    = _thread->_ParkEvent;
2100   _active   = false;
2101   assert(_event != nullptr, "invariant");
2102 }
2103 
2104 void ObjectWaiter::wait_reenter_begin(ObjectMonitor * const mon) {
2105   _active = JavaThreadBlockedOnMonitorEnterState::wait_reenter_begin(_thread, mon);
2106 }
2107 
2108 void ObjectWaiter::wait_reenter_end(ObjectMonitor * const mon) {
2109   JavaThreadBlockedOnMonitorEnterState::wait_reenter_end(_thread, _active);
2110 }
2111 
2112 inline void ObjectMonitor::AddWaiter(ObjectWaiter* node) {
2113   assert(node != nullptr, "should not add null node");
2114   assert(node->_prev == nullptr, "node already in list");
2115   assert(node->_next == nullptr, "node already in list");
2116   // put node at end of queue (circular doubly linked list)
2117   if (_WaitSet == nullptr) {
2118     _WaitSet = node;
2119     node->_prev = node;
2120     node->_next = node;
2121   } else {
2122     ObjectWaiter* head = _WaitSet;
2123     ObjectWaiter* tail = head->_prev;
2124     assert(tail->_next == head, "invariant check");
2125     tail->_next = node;
2126     head->_prev = node;
2127     node->_next = head;
2128     node->_prev = tail;
2129   }
2130 }
2131 
2132 inline ObjectWaiter* ObjectMonitor::DequeueWaiter() {
2133   // dequeue the very first waiter
2134   ObjectWaiter* waiter = _WaitSet;
2135   if (waiter) {
2136     DequeueSpecificWaiter(waiter);
2137   }
2138   return waiter;
2139 }
2140 
2141 inline void ObjectMonitor::DequeueSpecificWaiter(ObjectWaiter* node) {
2142   assert(node != nullptr, "should not dequeue nullptr node");
2143   assert(node->_prev != nullptr, "node already removed from list");
2144   assert(node->_next != nullptr, "node already removed from list");
2145   // when the waiter has woken up because of interrupt,
2146   // timeout or other spurious wake-up, dequeue the
2147   // waiter from waiting list
2148   ObjectWaiter* next = node->_next;
2149   if (next == node) {
2150     assert(node->_prev == node, "invariant check");
2151     _WaitSet = nullptr;
2152   } else {
2153     ObjectWaiter* prev = node->_prev;
2154     assert(prev->_next == node, "invariant check");
2155     assert(next->_prev == node, "invariant check");
2156     next->_prev = prev;
2157     prev->_next = next;
2158     if (_WaitSet == node) {
2159       _WaitSet = next;
2160     }
2161   }
2162   node->_next = nullptr;
2163   node->_prev = nullptr;
2164 }
2165 
2166 // -----------------------------------------------------------------------------
2167 // PerfData support
2168 PerfCounter * ObjectMonitor::_sync_ContendedLockAttempts       = nullptr;
2169 PerfCounter * ObjectMonitor::_sync_FutileWakeups               = nullptr;
2170 PerfCounter * ObjectMonitor::_sync_Parks                       = nullptr;
2171 PerfCounter * ObjectMonitor::_sync_Notifications               = nullptr;
2172 PerfCounter * ObjectMonitor::_sync_Inflations                  = nullptr;
2173 PerfCounter * ObjectMonitor::_sync_Deflations                  = nullptr;
2174 PerfLongVariable * ObjectMonitor::_sync_MonExtant              = nullptr;
2175 
2176 // One-shot global initialization for the sync subsystem.
2177 // We could also defer initialization and initialize on-demand
2178 // the first time we call ObjectSynchronizer::inflate().
2179 // Initialization would be protected - like so many things - by
2180 // the MonitorCache_lock.
2181 
2182 void ObjectMonitor::Initialize() {
2183   assert(!InitDone, "invariant");
2184 
2185   if (!os::is_MP()) {
2186     Knob_SpinLimit = 0;
2187     Knob_PreSpin   = 0;
2188     Knob_FixedSpin = -1;
2189   }
2190 
2191   if (UsePerfData) {
2192     EXCEPTION_MARK;
2193 #define NEWPERFCOUNTER(n)                                                \
2194   {                                                                      \
2195     n = PerfDataManager::create_counter(SUN_RT, #n, PerfData::U_Events,  \
2196                                         CHECK);                          \
2197   }
2198 #define NEWPERFVARIABLE(n)                                                \
2199   {                                                                       \
2200     n = PerfDataManager::create_variable(SUN_RT, #n, PerfData::U_Events,  \
2201                                          CHECK);                          \
2202   }
2203     NEWPERFCOUNTER(_sync_Inflations);
2204     NEWPERFCOUNTER(_sync_Deflations);
2205     NEWPERFCOUNTER(_sync_ContendedLockAttempts);
2206     NEWPERFCOUNTER(_sync_FutileWakeups);
2207     NEWPERFCOUNTER(_sync_Parks);
2208     NEWPERFCOUNTER(_sync_Notifications);
2209     NEWPERFVARIABLE(_sync_MonExtant);
2210 #undef NEWPERFCOUNTER
2211 #undef NEWPERFVARIABLE
2212   }
2213 
2214   _oop_storage = OopStorageSet::create_weak("ObjectSynchronizer Weak", mtSynchronizer);
2215 
2216   DEBUG_ONLY(InitDone = true;)
2217 }
2218 
2219 void ObjectMonitor::print_on(outputStream* st) const {
2220   // The minimal things to print for markWord printing, more can be added for debugging and logging.
2221   st->print("{contentions=0x%08x,waiters=0x%08x"
2222             ",recursions=" INTX_FORMAT ",owner=" INTPTR_FORMAT "}",
2223             contentions(), waiters(), recursions(),
2224             p2i(owner()));
2225 }
2226 void ObjectMonitor::print() const { print_on(tty); }
2227 
2228 #ifdef ASSERT
2229 // Print the ObjectMonitor like a debugger would:
2230 //
2231 // (ObjectMonitor) 0x00007fdfb6012e40 = {
2232 //   _metadata = 0x0000000000000001
2233 //   _object = 0x000000070ff45fd0
2234 //   _pad_buf0 = {
2235 //     [0] = '\0'
2236 //     ...
2237 //     [43] = '\0'
2238 //   }
2239 //   _owner = 0x0000000000000000
2240 //   _previous_owner_tid = 0
2241 //   _pad_buf1 = {
2242 //     [0] = '\0'
2243 //     ...
2244 //     [47] = '\0'
2245 //   }
2246 //   _next_om = 0x0000000000000000
2247 //   _recursions = 0
2248 //   _EntryList = 0x0000000000000000
2249 //   _cxq = 0x0000000000000000
2250 //   _succ = 0x0000000000000000
2251 //   _Responsible = 0x0000000000000000
2252 //   _SpinDuration = 5000
2253 //   _contentions = 0
2254 //   _WaitSet = 0x0000700009756248
2255 //   _waiters = 1
2256 //   _WaitSetLock = 0
2257 // }
2258 //
2259 void ObjectMonitor::print_debug_style_on(outputStream* st) const {
2260   st->print_cr("(ObjectMonitor*) " INTPTR_FORMAT " = {", p2i(this));
2261   st->print_cr("  _metadata = " INTPTR_FORMAT, _metadata);
2262   st->print_cr("  _object = " INTPTR_FORMAT, p2i(object_peek()));
2263   st->print_cr("  _pad_buf0 = {");
2264   st->print_cr("    [0] = '\\0'");
2265   st->print_cr("    ...");
2266   st->print_cr("    [%d] = '\\0'", (int)sizeof(_pad_buf0) - 1);
2267   st->print_cr("  }");
2268   st->print_cr("  _owner = " INTPTR_FORMAT, p2i(owner_raw()));
2269   st->print_cr("  _previous_owner_tid = " UINT64_FORMAT, _previous_owner_tid);
2270   st->print_cr("  _pad_buf1 = {");
2271   st->print_cr("    [0] = '\\0'");
2272   st->print_cr("    ...");
2273   st->print_cr("    [%d] = '\\0'", (int)sizeof(_pad_buf1) - 1);
2274   st->print_cr("  }");
2275   st->print_cr("  _next_om = " INTPTR_FORMAT, p2i(next_om()));
2276   st->print_cr("  _recursions = " INTX_FORMAT, _recursions);
2277   st->print_cr("  _EntryList = " INTPTR_FORMAT, p2i(_EntryList));
2278   st->print_cr("  _cxq = " INTPTR_FORMAT, p2i(_cxq));
2279   st->print_cr("  _succ = " INTPTR_FORMAT, p2i(_succ));
2280   st->print_cr("  _Responsible = " INTPTR_FORMAT, p2i(_Responsible));
2281   st->print_cr("  _SpinDuration = %d", _SpinDuration);
2282   st->print_cr("  _contentions = %d", contentions());
2283   st->print_cr("  _WaitSet = " INTPTR_FORMAT, p2i(_WaitSet));
2284   st->print_cr("  _waiters = %d", _waiters);
2285   st->print_cr("  _WaitSetLock = %d", _WaitSetLock);
2286   st->print_cr("}");
2287 }
2288 #endif
--- EOF ---